LI E> RAR.Y OF THE UNIVERSITY Of ILLINOIS G30.7 ho.354-3G3 cop. 2. AGRICULTURE NOTICE: Return or renew all Library Materials! The Minimum Fee for each Lost Book Is $50.00. The person charging this material is responsible for its return to the library from which it was withdrawn on or before the Latest Date stamped below. Theft, mutilation, and underlining of books are reasons for discipli- nary action and may result in dismissal from the University To renew call Telephone Center, 333-8400 UNIVERSITY OF ILLINOIS LIBRARY AT URBANA-CHAMPAIGN APR 2 8 20il5 LI61 O-1096 Corn Diseases In Illinois , THEIR EXTENT,NATURE, AND CONTROL BY BENJAMIN KOEHLER AND JAMES R.HOL.BERT UNIVERSITY OF ILLINOIS AGRICULTURAL EXPERIMENT STATION BULLETIN 354 In Cooperation With Office of Cereal Crops and Diseases. Bureau of Plant Industry. U 5 Department of Agriculture CORN DISEASES IN ILLINOIS BY BENJAMIN KOEHLER AND JAMES R. HOLBERT UNIVERSITY OF ILLINOIS AGRICULTURAL EXPERIMENT STATION URBANA, ILLINOIS September, 1930 UNIVERSITY OF ILLINOIS I! PRESS II 10M 9-30 671 CONTENTS PAGE INTRODUCTION 5 NATURE OF PLANT DISEASES 6 DISTRIBUTION OF CORN DISEASES IN ILLINOIS 10 METHODS OF DISEASE CONTROL 18 Sanitation 18 Crop Rotation 19 Soil Management 20 Developing Disease-Resistant Strains 22 Selecting Disease-Resistant and Nearly Disease-Free Seed 26 Seed Treatment 37 CAUSES OF DEAD SEED 42 SEEDLING DISEASES 43 General Considerations 43 Diplodia Seedling Disease 46 Gibberella Seedling Disease 55 Fusarium Seedling Disease 60 Basisporium Seedling Disease 63 Scutellum Rot Disease 67 Penicillium Seedling Disease 72 Aspergillus Seedling Disease 74 Sclerospora Seedling Disease 77 Py thium Seedling Disease 77 GENERAL DISEASES OF THE AERIAL PARTS 78 Black Bundle Disease 78 Bacterial Wilt (Stewart's Disease) 81 Common Smut 84 Leafy Abnormalities of Tassels and Ears 87 ROOT ROTS 89 General Considerations 89 Pythium Root Rot 91 Malnutritional Root Rot 93 STALK ROTS 94 Bacterial Stalk Rot 94 Diplodia Stalk Rot 96 Other Stalk Rots and Injuries 98 LEAF DISEASES AND DEFECTS 101 Rust 101 Brown Spot 103 Purple Sheath Spot 105 Helminthosporium Leaf Blight 107 Holcus Bacterial Spot 109 Leaf Firing 109 Heritable Chlorophyl Deficiencies 110 Rolled Leaves 112 EAR ROTS AND OTHER EAR DEFECTS 113 General Considerations 113 Diplodia Ear Rot 114 Gibberella Ear Rot 117 Fusarium Ear Rot 118 Basisporium Ear Rot 120 Penicillium Ear Rot (Blue Mold) 123 Crown Crack or Pop 123 Silk Cut 124 Defective Endosperm 124 Chaffy Ears 126 Failure of Fertilization 126 Mechanical Injury 127 Storage Rots 128 Damage from Feeding Rotten Corn 129 FUNGI AND DISEASE SYMPTOMS ON THE GERMINATOR 131 Place of Germination Test in Corn Improvement 131 Operating the Germinator 132 Importance of Seedling Vigor 135 Recognizing Disease Symptoms 135 Rhizopus species 136 Fusarium moniliforme 141 Cephalosporium acremonium 143 Diplodia zeae 145 Gibberella saubinetii 147 Penicillium species 147 Aspergillus species 148 Basisporium gallarum 149 Alternaria species 151 Other organisms 151 SUMMARY 152 LITERATURE CITED 155 GLOSSARY 160 INDEX.. . 163 CORN DISEASES IN ILLINOIS By BENJAMIN KOEHLER and JAMES R. HoLBERT 1 is the major farm crop in Illinois. The area devoted to in this state during the last five years has averaged approxi- mately 8,700,000 acres a year. This is more than the combined acre- age devoted to oats, wheat, and barley. Furthermore the cash value of the corn crop is practically twice that of the combined value of the small grain crops just mentioned. Unfortunately corn also holds very nearly first rank in the number of diseases that attack it and in the losses caused thereby. Some of the diseases have as yet re- ceived little study. Many of them cause injury of such a nature that losses to yield of grain are very hard to estimate. In a bulle- tin published by the Illinois Station in 1924, 46 * it was stated that all the diseases besetting the corn crop in Illinois cause an average annual loss of at least twenty percent. In the light of further in- vestigations this figure appears to be a very conservative estimate. Some corn diseases are very conspicuous. Every corn grower is well acquainted with the ear rots and smut. He usually considers these as inevitable. There is a considerable number of other equally important diseases that weaken the plant and reduce the yield but cause no conspicuous external symptoms. Such diseases have, for the most part, escaped the grower's notice. The material in this bulletin is designed especially to give the agricultural teacher and student, the farm adviser, and the inter- ested farmer specific information concerning the extent and nature of corn diseases in this state, how they may be recognized, and how they may be held in check in so far as practical control measures are known. While it is impossible at the present time, even experi- mentally, to grow corn plants in any number to maturity free from disease, an important saving by partial disease control is available to all. Probably present losses could be cut in half by the applica- tion of methods already developed and known to be effective. 'BENJAMIN KOEHLER, Assistant Chief in Crop Pathology, Department of Agronomy, Illinois Agricultural Experiment Station; JAMES R. HOLBERT, Senior Agronomist, Office of Cereal Crops and Diseases, Bureau of Plant In- dustry, U. S. Department of Agriculture. These figures refer to literature citations on pages 155 to 159. 6 BULLETIN No. 354 [September, The information presented here concerns dent corn principally, tho in general the same diseases occur on all the different kinds of maize, or Indian corn (Zea mays), namely, sweet, pop, flint, and flour corn, sweet corn usually being the most susceptible. Effort has been made to present the discussions in simple lan- guage. Nevertheless, for the sake of accuracy and brevity, certain technical terms have to be used. The meanings of such words are explained in the glossary at the end of the publication. Each topic has been organized as a more or less independent unit. While this arrangement has necessitated some slight repetition between sections, the advantage to the reader is obvious. Facts concerning the be- havior of corn diseases on the germinator are concentrated in the last part of the bulletin. The authors have drawn freely upon material published by other investigators as well as upon their own experiences and observa- tions. Literature references are given for some of the most impor- tant of these contributions, especially to the relatively recent ones. NATURE OF PLANT DISEASES Plant diseases are abnormal or unhealthy conditions of the plant or any of its parts that interfere with the natural functions or de- velopment. Such conditions may be brought about chiefly by: (1) fungous infection; (2) bacterial infection; (3) virus infection; (4) insect infection or poisoning; or (5) unfavorable environmental conditions. There are still other causes, but those mentioned have been found to be responsible for corn diseases. Fungous Infection. Fungi cause the greatest number of known corn diseases. A large number of fungi (Fig. 1) resemble weeds in some respects in that they have organs corresponding to stems (aerial hyphae and conidiophores) , roots (submerged hyphae and rhizoids), and seeds (spores). The outstanding difference between fungi and weeds is that the fungi have no leaves or green tissue, and therefore they cannot live independently as green plants can but must obtain their food from organic matter, dead or alive, just as animals do. When they attack live plants, they usually cause disease. Fortunately only relatively few of the two hundred thousand odd species of existing fungi are parasitic. Most of them are limited to dead organic matter for their food. 1930] CORN DISEASES IN ILLINOIS Some fungi can be seen only with a microscope, while others, as for instance the fungi (molds) causing corn ear rots, can be seen with the naked eye. Many of the fungi that attack live plants, FIG. 1. A FUNGUS PLANT, PENICILLIUM, GREATLY ENLARGED, ILLUSTRATING THE VARIOUS PARTS: (a) SPORES OR CONIDLA, (6) CONIDIOPHORES, (c) MYCELIUM. (Semidiagrammatic) In a typical Penicillium colony there are many more stalks than here shown and each stalk has more branches and bears more spores. To the naked eye the whole colony looks like a dusty, felty mass. There are many kinds of fungi. The differences they exhibit may be just as great as differences in the higher plants, for example, those between the dandelion and the oak. such as Ustilago zeae (one of the smut fungi of corn) , are able to attack only the one crop, in this case corn. On the other hand, Gibberella saubinetii attacks not only corn but a number of other cereal crops also. Most of the fungi that attack live plants will 8 BULLETIN No. 354 [September, grow also on suitable dead organic matter, but some others, such as corn rust, will grow and produce their spores only on live plants. Fungus spores develop in a variety of ways, depending on the species of fungus. One common type develops its spores out in the air free from any protection, as shown in Fig. 1. Another type produces its spores in sacs or capsules, as shown in Fig. 25. While an individual spore is invisible to the naked eye, the capsules con- taining the spores (sporangia, pycnidia, or perithecia) can usually be readily seen. The former type of spore production is best adapted for rapid spread of the fungus during the summer, while the latter in many cases is better adapted to carrying the fungus thru adverse conditions, such as winter weather, because the spores are protected. Some fungi produce both types of spores. There are wide variations in both these types of spore production, and there are still other types which will not classify under either of those just mentioned. The spores of fungi are carried by the wind, drainage water, insects, larger animals, and farm implements. When dry, some of them will remain viable for many years. Most of the corn- disease fungi live from one season to the next in the old corn refuse left on the fields. In the following season they produce spores which are scattered broadcast by the wind and infect the new crop. Some others are able to live from year to year in the soil apart from the corn refuse. A number are also able to live over winter in the seed corn and cause seedling diseases when the seed is planted. Bacterial Infection. Bacteria cause several diseases in corn. These are very simple organisms, being composed of only one cell, as shown in Fig. 2. They are so small that a high-powered micro- scope is necessary in order to see them. The cells of bacteria that cause plant disease are, with few exceptions, all rod-shaped. In some species these rods have no provision for independent locomo- tion, while in others the rods are equipped with one or several hair- like growths by the movements of which the rod is able to swim about. Spherical and spiral shaped bacteria occur also, but most of these live only on dead organic matter. As is true in the case of fungi, most of the many species of bacteria are not parasitic, only certain species being troublesome in this respect. Bacteria are carried from place to place and from one season 1930} CORN DISEASES IN ILLINOIS 9 to another much like the spores of fungi. Many of the parasitic species are able to attack only one particular species of plant. When they come in contact with the right plant and moisture and temperature conditions are favorable, some of these bacteria are able to enter the plant tissues thru the pores in the leaves. Other species of bacteria cannot do this so readily but are more dependent on plant injuries such as insect bites, frost cracks, etc., for gaining entrance to the plant tissues. Still others are carried over from one generation to the next in the seed. As these bacteria come in con- tact with water and the right food, they grow to mature size. Then FIG. 2. BACTERIA OF SEVERAL TYPES GREATLY ENLARGED The many species of bacteria causing diseases may be placed in the four groups, or genera, shown above: (a) Aplanobacter; (6) Bacterium; (c) Ba- cillus; and (d) Micrococcus, according to Smith's classification. Only the first three, however, seem to be important as plant pathogens. each cell divides into two, and each part again grows to mature size, and so on. In some cases such multiplication may occur as rapidly as several times an hour. Virus Infection. There is a virus disease of corn known as corn mosaic. This disease occurs in the southern states, but has not yet been found in Illinois. The virus occurs in the plant sap, but cannot be seen with a microscope. There has been much con- jecture about its nature. If a very minute portion of the sap from a diseased plant is injected into a healthy plant, the disease will develop as in the first plant. It can thus be carried from one plant to another indefinitely. This indicates that the causal agent in the sap is able to increase in quantity and thus seems to be alive. On the other hand, there is a possibility that a virus is simply a chemical structure perhaps somewhat analogous to an enzyme. Many virus diseases of plants and animals are known. Studies of these diseases are under way at various institutions. Insect Infection or Poisoning. When insects cause mechanical injury to plants, the condition is usually not considered as disease, but when such injury is accompanied by injurious malformations 10 BULLETIN No. 354 [September, of the plants, or when the insect bites cause extensive physiological disturbances, then it seems evident that the plants must be con- sidered diseased. In the latter case a toxin or poison appears to have been injected by the insect, for wilting or blighting may soon occur. Diseases caused by such toxins or poisons are known to occur in several kinds of plants, and it is probable that corn plants are affected by injuries of this kind. In the south Atlantic states injury to corn by the eel-worm (root knot) disease has been re- ported. A tiny worm, microscopic in size, bores into the roots. This causes a swelling and abnormal behavior of the roots and conse- quently reduces the growth above ground. Physiological Disturbances. The normal physiological behavior of plants is sometimes interfered with by environmental factors. A small amount of foreign gas in the air, as for instance sulfur dioxid, will cause wilting and dying of leaves. The gases emanating from some industrial plants have sometimes been under suspicion and in some cases have no doubt caused serious trouble. Unbalanced soil fertility may cause well-marked disease symptoms. On corn this is especially true in some parts of southern Illinois, where the addition of considerable nitrogenous fertilizer on the potash-de- ficient soil gives disastrous results. The ears in the latter case fail to mature and thus remain very chaffy. The stalks often are stunted and fall down early owing to unusual susceptibility to root and stalk rot under these conditions. DISTRIBUTION OF CORN DISEASES IN ILLINOIS All the diseases reported herein are, with a few exceptions known to occur thruout the state. Nevertheless differences in se- verity no doubt do occur with different geographical locations. For the most part accurate survey data on this feature are lacking, and where they are available they extend over only a few years. But a study of the regional influences that probably affect disease prevalence should be of value, and some of the factors will here be considered. It should be borne in mind, however, that all these fac- tors interact on one another and that seldom is one factor alone responsible for a certain result. Effect of Temperature. As the state of Illinois is nearly four hundred miles in length, the southern end is considerably warmer 1930} CORN DISEASES IN ILLINOIS 11 than the northern region. As winter temperatures are not of so much concern as summer temperatures in this discussion, the aver- age temperature during the corn growing period only is mapped in Fig. 3. It will be seen that the average summer temperature in the southern group of counties is ten degrees higher than it is in the northeastern part of the state. Furthermore the data 94 * show that the temperature in the northern section is considerably more variable than in the southern section. The highest temperature recorded in FIG. 3. TEMPERATURE ZONES IN ILLINOIS, MAY TO SEP- TEMBER INCLUSIVE The warmer temperatures in the southern half of the state encourage the development of certain diseases which are comparatively rare or even unknown in the northern section. Some other dis- eases are not influenced in that way. (Sections indicated by heavy lines estab- lished by the U. S. Weather Bureau. Temperature areas plotted from U. S. Weather Bureau data. 85 *) MEAN TEHPERATI! MAY-SEPT. the former is 112 F. while the highest in the latter is 115 F., a difference of only 3 degrees. There are periods when the maximum daily temperature in the north is just as high as in the south, but in the northern sections the nights usually are cooler and the warm periods are irregular, being more or less interspersed with cool peri- ods. In the southern section the weather is more nearly constantly warm. Several diseases are known to be influenced by these differences in temperature, and no doubt there are still others that also are influenced. The "brown spot" disease (page 103) causes considerable loss in the southern states but diminishes in importance northward, the northern limit of its distribution being somewhere in the neigh- 12 BULLETIN No. 354 [September, borhood of the northern boundary of Illinois. Within Illinois it has been noted to be of greater prevalence in the southern than in the northern part. Warm moist weather is necessary for infection to take place. Bacterial stalk rot (page 94) is another disease that is preva- lent in the South, but has been observed no farther north than central Illinois. Like the brown spot disease, it too requires very warm moist weather in order to become established. The black bundle disease has been observed to be more preva- lent in the southern and central sections of the state than in the TABLE 1. PERCENTAGE OF INFECTED KERNELS IN ILLINOIS UTILITY SHOW CORN (Five-year average, 1925 to 1929, of all yellow and white 10-ear entries at the State Utility Corn Show, Urbana) Kind of corn Disease infection Northern 1 section Central 1 section Southern 1 section Yellow Scutellum rot perct. 8.12 perct. 9.33 perct. 10.40 1 95 1 68 2 18 Gibberella saubinetii 1.49 1.13 1.56 Fusarium moniliforme 9.01 9.24 14.52 6 63 8 59 5.68 White Scutellum rot 10.39 12.42 15.13 Diplodia zeae 2.47 1.95 2.97 Gibberella saubinetii 2.36 .95 2.16 Fusarium moniliforme 8.43 12.36 15.02 Cephalosporium acremonium 3.98 4.48 5.02 ^ee map, Fig. 3. northern. It is not known whether or not this is due to differences in temperature. During two years the Illinois State Natural History Survey (page 78) obtained data on the prevalence of this disease in a manner that fairly represents the whole state. Their data for 1924 showed 2.8 percent diseased plants in the northern, 6.8 in the central, and 5.3 in the southern section, and for 1926 1.2, 3.4, and 5.9 percent respectively. Data secured from entries at the State Utility Corn Show over a period of five years, in an entirely different manner, corroborate these findings (Table 1). The ears entered in this show from the central section of the state carried a higher percentage of Cephalosporium than those from the northern section, in both yellow and white corn. In yellow corn the percentage of infection decreased in the southern section, but in white corn it increased still further over what it was in the central section. 1930] CORN DISEASES IN ILLINOIS 13 Another important consideration in connection with tempera- ture is the duration of the frost-free period. Maps illustrating the average time of the last recorded frost in spring and first recorded frost in fall are shown in Fig. 4. It is obvious that the season is shortest in the northern part of the state. This means that a shorter season corn is necessary there than is used in the central or southern lst-5t(. FIG. 4. AVERAGE DATES OF KILLING FROST IN ILLINOIS AS REPORTED BY COLLABORATORS OF THE U. S. WEATHER BUREAU"* Because the length of the growing season varies in different parts of the state, the corn types adapted to these different sections show many variations, among which appears to be their ability to resist certain diseases. The types grown in the shorter season of the northern section have been found to be more resistant to scutellum rot and Fusarium moniliforme ear infection. part of the state. In how far the difference in length of season actually is a factor affecting prevalence of disease is not known. The fact that different varieties are used in the areas of different frost- free periods no doubt has some influence on disease preva- lence, as will be discussed under corn types. Furthermore, as there is a greater tendency to plant in cold soil in the northern section on account of the shorter season, there would consequently be more 14 BULLETIN No. 354 [September, trouble from certain seedling diseases, especially if the seed is not treated. The weather data on killing frosts as plotted in Fig. 4 are based on reports up to 1921 made by collaborators of the U. S. Weather Bureau. 94 * In general it may be expected that the grow- ing season for corn is not so long as here indicated. FIG. 5. SUMMER RAINFALL, MAY TO SEPTEMBER INCLUSIVE, AS COMPARED WITH ANNUAL RAINFALL The amount of annual rainfall increases progressively from the northern section of the state to the southern extremity. In summer, however, when the corn makes its principal growth, the rainfall is lightest in the eastern and heaviest in the western region. (Plotted from U. S. Weather Bureau data. 95 *) In many parts of the southern half of the state another factor enters. Owing to certain soil conditions the limiting factor in the spring is not frost but rather the soil moisture. Many farmers there begin planting corn later than those in the central section because the soil is too wet to start earlier. In that case only the additional length of the season in fall is of consequence. Further- more the soil is fairly warm by the time the farmers are able to plant, so that they would be expected to have less trouble with 1930] CORN DISEASES IN ILLINOIS 15 seedling diseases if it were not for the high soil moisture which more or less counteracts the favorable temperature. Effect of Moisture. High atmospheric moisture and also high soil moisture favor the development of many diseases. It is well known that the amount of annual rainfall increases from the north- ern to the southern part of the state (Fig. 5). But in a study of diseases on the growing corn plant we are concerned primarily with summer rainfall. Therefore the May to September rainfall was mapped and it was found that in the summer the rainfall is heaviest in the western region and lightest along the eastern region, as shown in Fig. 5. The heavy annual rainfall in the southern section is due largely to the large amount of precipitation occurring in that region from October to April. Among the diseases favored by high moisture are some of the seedling diseases, stalk rots, and ear rots. Atmospheric moisture conditions during the fall also are of con- siderable importance in determining the final quality of grain pro- duced. After the ears are mature or after the plants have been killed by cold, the quicker the ears become dry the less rot is apt to occur. When it rains much of the time during the fall months, especially when the rain is accompanied by mild tempera- ture, severe losses from ear rots in the field or in newly cribbed corn are likely to take place. Danger of such losses are greatest in the southern section of the state, for, as shown in Fig. 6, the rainfall in that section during the fall is considerably greater than in the central or northern sections, the northern section having the lowest rainfall of all during that time. Among the diseases that are favored by high moisture are some of the ear rots, stalk rots, and seedling diseases. Effect of Corn Types. A state corn show, 71 * sponsored by the Illinois Crop Improvement Association in cooperation with the Uni- versity of Illinois, has been held annually during the past eight years. A germination test has been made of every ear entered, and during the last five, years data on all diseases occurring in this corn, as observed on the germinator, have been recorded as accurately as possible. Altho the percentages of disease infection in this show corn were no doubt considerably lower than occur in average farm seed corn, yet the data supply a basis for comparing the relative extent of seed infection in different parts of the state. It will be seen from Table 1 that the percentage of scutellum rot and Fu- 16 BULLETIN No. 354 [September, sarium moniliforme increases progressively from the northern sec- tion to the southern section in both yellow and white corn. This NORTHERN SECTION INN minim MINIM III UAN. I FEB I MAP I APR I MAY UUNE I JULY I AUG I SEPT I Per I Nov. I Dec I CENTRAL SECTION Illllllllll Illllllllll JAN. FEB MAP. I APR. I MAY IUNE I JUL I AUG. I ri Per I ov I SOUTHERN SECTION ii Mini II Illlll II Illlll UAN I FLB I MAPI.APR. I jlAYlJuNElJuLY I AUG. I SEPT! OCT FIG. 6. MONTHLY RAINFALL IN THREE SECTIONS OF ILLINOIS The northern section has a favorable fall for the ripening and drying of corn. Heavy rains in the winter and early spring in the southern section cause corn planting to be delayed too long for best results, and when it is planted the soil moisture often is still high, a condition which encourages seedling diseases. (Plotted from U. S. Weather Bureau data. 95 *) difference seems to be due to the fact that altho all the corn in this show was, in one sense, of the utility type, the earlier-maturing corn CORN DISEASES IN ILLINOIS 17 from the northern region is more horny in composition than that to the southward, which has a longer growing period. In average farm seed corn the difference would probably be still greater than in the show corn from which these data were taken. w*:/.fe::4& &&:*j CORN ACREAGE 1928 FIG. 7. CORN ACREAGE, 1928, EACH Dor REPRESENTING 5,000 ACRES The more extensively corn is cropped, the more prevalent and destruc- tive most of the corn diseases tend to become. Corn is not so extensively grown in the southern third of the state as in the northern two-thirds, but still no county has less than 15,000 acres in corn. (Data taken from Circ. 385, Illinois Crop and Livestock Statistics, U. S. Dept. Agr. and 111. Dept. Agr. cooperating.) In these show exhibits the white corn proved more suscep- tible to seedling injury by scutellum rot and Diplodia zeae infec- tion than the yellow corn. In the case of Cephalosporium (black bundle disease) the situation was reversed, except that here an error may possibly have crept in because Cephalosporium infection. 18 BULLETIN No. 354 [September, is sometimes more difficult to detect on kernels of white corn on the germinator than on yellow corn. Effect of Intensity of Cropping. Other factors being similar, one would expect the most damage from corn diseases in areas where corn is cropped most intensively. Altho corn root rots, apart from the seedling diseases, have as yet received little study in this state, especially from the standpoint of their distribution, judging from what is known about soil-borne diseases of some other plants, the intensity of cropping is an important factor in determining the amount of damage caused by these diseases. On account of the lighter cropping of corn in the southern third of Illinois (Fig. 7), there should be less corn refuse from the previous crops scattered about, and consequently one might ex- pect less prevalence of certain diseases that are caused by wind- blown spores produced on old diseased refuse. Ear infection or ear rot is caused in this way. But apparently some other factors are active in counteracting such an effect, for Table 1 shows no such relationship. The warm, moist fall weather probably is a factor especially conducive to ear infection in this region. METHODS OF DISEASE CONTROL Not all diseases can be controlled in the same way, but a con- siderable number of corn diseases can be kept in check by the application of the same general methods of attack. These methods will be considered here in detail, so that a full discussion will not be necessary in connection with each specific disease. While ordi- narily no one disease appears sufficiently destructive to warrant extensive applications of control measures, it is a fact that careful attention to a well-rounded program of control involving sanitation, crop rotation, soil management, breeding for disease resistance, plant and ear selection, seed treatments and, where feasible, a germination test, tends to check most of the major diseases, so that general control practices as set forth under the following headings are well worth while. SANITATION By sanitary measures are meant such practices as tend to elim- inate germs, spores, or other inocula that cause disease. As yet such measures are not employed to a great extent for the control 1930} CORN DISEASES IN ILLINOIS 19 of cereal diseases, but it is thought that irtany diseases could be held in check by such practices, especially if carried out over a wide territory. In the case of corn the complete removal or turning under of all cornstalks and rotten ears before the new season opens would no doubt be a great help in reducing corn ear rots. These diseases are caused by spores produced on the old corn refuse and carried by the air currents to the new crop. Thoro plowing may also be expected to reduce smut and some other diseases. When the old refuse is covered with soil, the disease-producing spores cannot get out into the air to infect the stalks and ears of the new crop. One difficulty about turning corn refuse under is that of keeping it ac- tually under the soil surface. When some of the undecayed stalks or ears are returned to the surface by the next year's plowing, there may possibly still be danger of this being a source of inoculum, altho the danger probably is not great. The application of this measure, even tho it cannot be carried out perfectly, promises to be of considerable help. When corn fodder or ears are fed, the diseases are likely to per- sist in the unconsumed stalks and cobs. When these are thrown into the manure, the same precautions about thoroly plowing them under ought to be observed. Unless turned under well, such manure should not be used where corn is to be planted that same year. As for the spores that are eaten, it has been shown that smut spores which have passed thru the digestive tracts of cows or horses, no longer are viable. 28 * CROP ROTATION A number of the organisms that cause corn diseases are able to live in the soil or on the soil surface for some time. Some of them are dependent on the presence of corn refuse. As soon as the corn refuse has decayed, these organisms seem to disappear. Some others are not dependent on corn refuse. One of these is smut. Under outdoor conditions it does not seem to live on or in the soil longer than one year. The smut spores cannot serve as inoculum when buried beneath the surface. Pythium possibly also persists in the soil in the absence of corn refuse, but this fungus has as yet re- ceived little study. Many observations leave no doubt that root rots are considerably aggravated by cropping corn on the same soil very frequently. It is believed that a rotation including corn only once in three or four years would be satisfactory from the stand- 20 BULLETIN No. 354 [September, point of disease control. This allows sufficient time for the old corn refuse to decay. It has been demonstrated fairly satisfactorily that corn plants are much more firmly rooted in such a rotation than where corn is cropped more frequently. 68 * Ear rots have been re- duced by the same practice. Very likely some other diseases also are held in check thereby to some extent. Under certain conditions, however, there may be other important considerations which make such a rotation impractical. SOIL MANAGEMENT Nutritional factors not only have a large influence on vigor of growth and yield of corn grain, but they also influence the preva- lence of diseases and the extent of the losses caused by them. Altho the relation of soil fertility to disease is not yet well understood, several general statements can be made. A high state of soil fertility hastens the development and ma- turity of corn. There is evidence to show that, other things being equal, corn ears are drier in the fall when they have been grown on soil of good productivity than when grown on less-fertile soil, and in some seasons the differences are striking. Ears with low moisture content are less likely to develop ear infections and ear rots in the field during the fall. Unless the moisture is low at husking time, ear rot is likely to develop in storage. While, as stated above, it is generally true that corn ears are drier in the fall when grown on soil of good productivity, the re- verse sometimes is true. Temperatures that do but little damage to corn growing on more-fertile soil sometimes kill corn growing on poor soil; and while ears produced on poor soil may be highest in moisture at the time the plants are killed, after this event they dry out more rapidly than do the ears on the better soil, where the plans are still functioning. When harvested later in the season, the ears from the plants killed early will have less moisture than those from the more vigorous plants that grew to better maturity. A lack of balance in the supply of plant-food materials may be a still greater handicap in the development of healthy corn plants than a low general level of fertility. The presence of a liberal sup- ply of nitrogen, for instance, when the amount of phosphorus or potassium, or both, is inadequate, is especially conducive to the development of certain diseases. With respect to phosphorus it has been shown that a lack of this element retards maturity, and con- 1930} CORN DISEASES IN ILLINOIS 21 sequently where phosphorus is low there is more likelihood of in- jury from ear rot. The phosphorus supply, it has been shown also, is a factor in determining the importance of seed infection with Fusarium moniliforme. In experiments where rock phosphate was applied, seed infection with this fungus has been found to be of less consequence to yield of grain than it was in the check plots that received no phosphate. 46 * An insufficient supply of potassium in relation to other plant- food materials also hinders proper maturation and thus increases the ear-rot hazard. When the potassium shortage is extreme, severe pathological conditions are likely to develop. Under some condi- tions the ears fail to develop properly and often dry out early in a loose, chaffy condition. This effect may be due in part to toxic conditions in the plant, and it may also result from failure of the plant to synthesize carbohydrates properly. Under some other con- ditions a lack of potassium may result in extensive root rot and sometimes also stalk rot, so that the plants remain stunted and fall to the ground during the latter part of the summer. A further dis- cussion of this condition will be found under "Mamutritional Root Rot," page 93. The application of agricultural limestone appears to be of con- siderable importance in correcting certain unfavorable conditions that sometimes occur in poorly drained soil that has an acid re- action and perhaps sometimes in other sour soils also. Limestone seems to convert the toxic substances to an insoluble or an inactive condition in which they are harmless. Very frequently liming causes the corn plants to stand up better than they do on similar land that is unlimed. 68 * The exact cause of this phenomenon has not been ascertained. There are indications that variations in the nutritional balance have a bearing on the occurrence or the severity of still other corn diseases than those mentioned, but there is not yet sufficient evi- dence available on this point to warrant a definite statement. In addition to the fertility of the soil, proper soil drainage and tillage also are of importance from the standpoint of disease control. While the various aspects of soil management that have been mentioned deserve careful attention, it must be emphasized that soil management is only one of the corner stones for disease control. In fact there are some corn diseases that seem to be aggravated by 22 BULLETIN No. 354 [September, good fertility, as, for instance, smut and some stalk rot diseases. That some seedling diseases are very active in highly productive soil is indicated by the fact that when the corn is grown on such land, seed treatments nearly always give the best increases in yield. Thus it is only when a well-rounded program for corn improvement is followed that satisfactory results are obtained. DEVELOPING DISEASE-RESISTANT STRAINS There is practically no evidence that any strains of corn are immune from any of the well-known corn diseases. Various strains and selections, however, grown under the same environmental con- ditions, may be damaged to widely different degrees by some dis- eases. Such differences, when due to the nature of the plants themselves, are called differences in resistance or susceptibility. The fact that there are certain hereditary differences in strains of corn and in individual corn plants, in their resistance or suscep- tibility to disease, is highly important from the standpoint of dis- ease control. The term disease resistance, however, must be clearly distin- guished from disease escape. To illustrate: Corn grown w r here much of the debris of a previous corn crop has been left on the ground may show more ear rot than where corn of the same strain has fol- lowed a legume. This difference may be due to the presence of fewer spores of ear rot pathogens under the latter circumstances. This is an example of disease escape. Sanitation, crop rotation, and soil conditions, already discussed, are all concerned with disease escape, as are also soil temperature, soil moisture, and certain other factors. Immunity from a disease means complete absence of dis- ease under all the natural conditions under which the plant may be grown, even where the pathogen is present and the environmental conditions are favorable for disease development. But, as stated above, immunity of corn to any of the well-known corn diseases probably does not exist, altho marked progress has been made in developing highly resistant strains, as discussed later. In order to obtain the highest yields and best quality of corn, it is well for the corn grower to use such practices as will permit the corn to escape disease so far as possible. When breeding for better disease resistance, however, it is necessary to use measures that are in some respects completely opposite to those that are recommended for growing the most profitable commercial crop. 1930} CORN DISEASES IN ILLINOIS 23 Selections should be made from corn which has been thoroly ex- posed to the diseases in the field and has proved resistant. A plant that has simply escaped disease may appear to be healthy and the ear from it may test free from disease on the germinator, and yet when the progeny of this plant is exposed to infection, the plants may become badly diseased. In other words, a disease-free ear will not necessarily produce healthy plants; the ear may be free from disease only because it has not been exposed to infec- tion and not because it is resistant to infection. The fundamental considerations for the development of disease resistance in corn are essentially the same whether open-pollinated or inbred strains are used. Open-Pollinated Strains. Strains of corn grown on a commer- cial scale at the present time are with few exceptions all open- pollinated. Cross-pollination is the natural process in corn. This is altered only when artificially controlled by man. In certain cases studied it was found that only 5 percent or less 34 ' 62> 112 * of the ker- nels on an ear were self-pollinated, that is, fertilized by pollen from the plant that developed the ear. The other kernels were fertilized by pollen from other plants. Pollen may be effective even after having been blown half a mile away. Cross-fertilization makes it more difficult to obtain and maintain disease-resistant strains. Being cross-pollinated, the ears that are selected will not breed true for the characters desired, and therefore selection must be kept up year after year. Thus selection toward better disease resistance is slow work but, nevertheless, considerable improvement can be and has been made. There are many named strains of open-pollinated corn on the market, but these names in themselves mean nothing with respect to disease resistance. The worth of a strain of corn can be esti- mated only when it is known with what ideals and care the strain was selected up to the time it was received. At the present time in Illinois the so-called "utility type" is more generally used, but still many farmers do their selection in a superficial manner and fail to take into consideration the various characters that tend to in- dicate disease resistance and freedom from disease. The term "utility type" has been adopted very generally thru- out Illinois to designate any open-pollinated variety of corn that has been selected with particular reference to disease resistance of 24 BULLETIN No. 354 [September, FIG. 8. UTILITY EAR TYPES Some of the important characteristics of utility ears are: good length, medium diameter, heavy weight in proportion to size, medium-smooth in- dentation, bright luster, horny kernel composition, a shank attachment that breaks off smoothly and is free from rot, freedom from weathering and mold, and plump, bright kernels with well-developed germs. the plant and ear and to inherent capacity to produce satisfactory yields of sound grain irrespective of whether or not the ears con- formed to any other standards such as straightness of the rows of kernels and uniformity of size and shape of ears. In Illinois this term had its origin about the time and in con- 19301 CORN DISEASES IN ILLINOIS 25 nection with the first State Utility Corn Show in 1921. The corn at this show was judged by what was then a new score card. The points on this score card and their relative weights represented the composite judgment of workers in the University of Illinois, the U. S. Department of Agriculture and, in addition, many corn breed- ers and corn growers. It was the aim of those workers to formu- late a score card that would call attention to and emphasize the physical characteristics that experimental evidence had shown to be associated, to a considerable extent, with disease resistance, better seed condition, and higher yields of sound corn. The score card included a germination test. This score card soon became known as the "Utility Score Card." Corn selected according to the standard set up in this score card is known as "utility type" corn (Fig. 8). Later this score card was modified somewhat and adopted by the Illinois Crop Improvement Association as the official score card for the Annual State Utility Corn Show. 71 * Since that time other corn score cards involving somewhat similar ideas have been suggested and in a few cases adopted by corn investigators of some other states. A good score card in which important ear and kernel characteristics are considered but in which the germination test is omitted has been proposed by Hughes and Robinson 50 * of Iowa. It may be pointed out here that there is considerable difference between "utility type show corn" and "utility type seed corn." Altho the former is the offspring of the latter, a number of the old corn show ideas have been retained (wisely or unwisely), so that considerable weight is given to uniformity and other characters which have little or no commercial value. Crosses of Inbred Strains. The U. S. Department of Agricul- ture, many of the state agricultural experiment stations, and a number of private corn growers' and business organizations are developing inbred strains of corn. A number of crosses between such inbred lines have proved highly resistant to some diseases (Fig. 54) as well as highly productive. There is much hope that superior crosses will be obtained that will be resistant to all the more important diseases as well as highly desirable from other standpoints. Single- and double-crossed seed from inbred lines, which is superior to open-pollinated seed in quantity and quality of grain which it produces when grown under certain climatic and 26 BULLETIN No. 354 [September, soil conditions, is already available from some seed houses. Progress apparently is being made yearly in the production of better inbred strains and crosses, and it seems likely that seed of these better crosses will be used to a considerable extent in the future. This method of breeding is still in the experimental stage, however, and many difficulties are still to be overcome. From the standpoint of developing disease-resistant strains by this method, the following considerations may be mentioned: 1. Resistance to the many corn diseases depends on many char- acters, both structural and functional. Inbreds that are resistant to one or several diseases have already been obtained, but resistance to a greater number or to all. of the more important diseases is desired. 2. The fact that there are different strains of pathogenic organ- isms increases the difficulty of breeding for disease resistance. It was found 7 ' 102 * that some inbred lines of corn that had been highly re- sistant to smut became very susceptible when a smut culture was introduced from another region. Physiologic strains are known to occur not only in corn smut but also in corn rust. 75> 102 * They may occur also in some other corn pathogens. Considerable variation is known to occur in the cultural behavior of various isolations of Fusarium moniliforme and Gibberella saubinetii. In how far these fungi exhibit physiologic specializations in their activities as path- ogens has not been adequately studied. 3. For the best results different crosses will probably have to be produced for different environmental conditions. Thus if a strain is developed that is highly resistant to most diseases, its use will likely be limited to restricted areas having similar soil and atmos- pheric environment, and other strains must be produced for other regions. What the ultimate size-limit of an area will be for a given strain cannot be predicted, but it probably will not be greater than, for instance, an area best adapted to a single strain of wheat and it may be considerably smaller. SELECTING DISEASE-RESISTANT AND NEARLY DISEASE-FREE SEED* Plant Selection. Given a strain of corn well adapted to local conditions, the first important consideration in the selection of 'The word "seed" is here used in its popular sense rather than in its exact botanical meaning. 1930] CORN DISEASES IN ILLINOIS 27 disease-resistant and nearly disease-free seed is the selection of plants that possess characters which we wish to propagate. Many important hereditary features, including resistance to certain dis- eases, or morphological weaknesses that allow disease organisms to enter, can be observed in the mother plant but not in the ear. Only after a satisfactory plant has been found should the ear be ex- amined to see whether it too appears satisfactory. Not too much attention should be given to ear characters at this time, because that can be taken care of better after the ears have been cured. Unfortunately many farmers pay too much attention to type of ear when selecting corn in the field and take too little time in scrutinizing the plant from which it came. Altho corn is cross- pollinated and one can examine the mother plant only, still by care- ful selection year after year considerable progress can be made. The corn should be allowed to mature well, in so far as weather conditions permit, before seed selections are made. The selections should be made before there is excessive damage from cold weather, altho a temperature just low enough to kill the leaves of plants more susceptible to cold injury, occurring before selections are made, may be of distinct advantage, for then selections can be made for resistance to cold injury as well as for resistance to dis- ease. It should be borne in mind, however, that even tho immature plants usually are less subject to damage by low temperature than are the more mature plants, they should not be selected for seed purposes. When a plant is injured by low temperature, the leaves or the affected portions of them have a dull, pale bluish-green color, as if they had been scalded. If examination is made shortly after the injury occurs, such leaves can be clearly distinguished from those that have died earlier, but usually after a few days have elapsed the "frosted" leaves, or portions of them, turn straw color, and it is not so easy to discern the exact cause of their death. However, even after practically all the leaves have been killed by low temperature, considerable difference in the health of a plant and its resistance to cold is indicated by the greenness of the stalk and by its firmness when pressed between the fingers. As husking by machinery is increasing in popularity, it becomes of greater importance than formerly to select strains that stand erect in the field until husking time. Selections for erect stalks can no doubt be made to best advantage late in the season, pos- sibly in November (Fig. 9). Such late selections should be made 28 BULLETIN No. 354 [September, in addition to those made earlier in the season and, for breeding purposes, the seed of these late selections should be planted sepa- rately from the earlier selections, for one cannot depend on getting good seed corn so late in the season every year. A breeding project FIG. 9. RESISTANCE TO STALK BREAKING Is INHERITED Two inbred lines of corn as they appeared at harvest time are shown above. The one on the left is very susceptible to stalk breaking, every ear usually being on the ground by the first week of November. The one on the right for the most part remains erect thruout the winter. Continuous selection in open-pollinated strains is also effective in increasing the tendency of corn to stand erect until husking time. cannot be completed in one year, and it will be necessary to re- select for stiff stalks every season in which weather conditions are favorable. Plant selection is of value only in proportion to the care and intelligence exercised in making it. Important Points in Making Plant Selections 1. The plants should be well anchored by the roots; they should stand erect. Plants that lean over are likely to have either considerable root rot or a weak root system. It is undesirable to propagate the tendency toward either one of these defects. 1930] CORN DISEASES IN ILLINOIS 29 2. The stalk and parts of the leaves should be green while the husks have turned straw color. Plants showing firing or dying of the leaves or any con- siderable reddish or purplish discoloration of leaves or stem, or plants severely injured by low temperatures should be avoided. Some of these conditions may be an indication of disease (Plate I) or may be associated with susceptibility to disease. 3. The plants should be free from smut. Susceptibility to this disease is inherited. 4. The ear should be supported by a sturdy, unbroken shank. Broken shanks frequently are diseased and the infection may extend into the ear. 5. It is of some advantage to have the shank so curved that the tip of the ear is inclined downward. Then the water will run off the husks as from the shingles of a roof. Less infection has been found in such ears than in those that stand upward. Care must be taken to see that they are inclined in natural growth and not because the shank is broken. 6. The husks should cover the ear well. This reduces the chances for ear infection. In some fields it is difficult to find well-covered ears. After several years of careful selection for long husks, it no longer becomes so hard to find them (Fig. 10). 7. The ears themselves should not be very large in circumference, as such ears dry slowly and therefore are open to disease infection for a longer period. Ears showing mold or insect injury should not be taken, for they would be culled out later. There are still other characters in type of plant and type of ear that the grower will want to consider, but as these are not directly concerned with disease resistance or the presence or absence of dis- ease, they are not within the province of this publication. Curing. After the seed ears have been selected they should be dried rapidly. Under some seasonal conditions when the corn is rather high in moisture and the weather conditions are not favor- able for drying, proper drying facilities are a serious problem on the average farm. Under such conditions a heated and well-venti- lated drying room is almost imperative. In some houses the room above the kitchen answers fairly well for this purpose. Hanging the corn in a shed is risky, for the disease molds spread rapidly in the damp ears and, furthermore, in case of a hard freeze the seed may be injured or killed. Some commercial equipment which assures forced ventilation at 100 to 110 F. seems very satisf ac- ton-. This temperature checks mold growth and is not hot enough to injure the seed. Under favorable seasonal conditions, on the other hand, there is no difficulty in curing the ears properly under ordinary farm conditions if good judgment is exercised. Weak light is desirable in the drying and storage room. Bright PLATE I A Plant prematurely dead on account of disease. B Plant maturing normally. In the diseased plant (A) the leaves are either dying or already dead and the ear is hanging down as the result of a crumpled and rotted shank. Corn produced on such a plant is light or chaffy. While it is evident that such ears are not good for seed purposes, there are in- termediate stages between A and B in which the ear may have a good appearance superficially and yet be physiologically immature and there- fore produce plants very susceptible to disease. In the healthy plant (B) the ear is maturing normally while the leaves and stalk are still green. Corn from such plants makes excellent ma- terial from which to select seed. 30 Corn Diseases in Illinois Plate I Illinois Agricultural Experiment Station 1H.10] CORN DISEASES IN ILLINOIS 31 FIG. 10. SCHEMATIC DRAWING SHOWING A LONGITUDINAL SECTION OF A CORN PLANT OF THE DENT VARIETY Note the rudimentary buds in the leaf axils beneath the ear. These are weak points thru which infection of the stalk often takes place. Note also how the husk covers the shank and ears, protecting these parts against in- fection as well as cold injury during short periods of low temperature. 32 BULLETIN No. 354 [September, light, especially direct sunlight, bleaches the ears so that it is im- possible to take the kernel luster into consideration when doing the final selecting. Hangers in which the ears are laid are preferable to those that have prongs on which the ears are stuck, for the shank attachment is taken into consideration when the ear is re-examined and therefore it should not be marred. Ear Selection (physical). The seed ears should be selected with care and discrimination after they have been dried or cured. Not every ear that is diseased or susceptible to disease can be detected and removed in this selecting or culling process, but by observing the following points the seed lot can be greatly improved. Points 1, 2, 3, 6, and 7, listed below, are concerned primarily with complete maturity of the ear. As disease infections, whether of the root, stalk, or ear, frequently arrest the final maturing stages, the completely matured ears are more likely to come from relatively disease-free plants. 46 * The new crop, when grown from such seed, will have greater resistance to certain diseases. Points 4, 5, and 8 are more directly concerned with disease symptoms. Important Points in Making Ear Selections 1. The kernel indentation should not be very rough (Fig. 8). In addition to indicating immaturity and the probability of a high percentage of soft starch, the outer tips of the rough kernels usually become broken in handling and this also is undesirable (page 127). 2. The ear should be outstanding in weight and solidity. Some practice is required in order to estimate the comparative weights of ears with suffi- cient accuracy to be of value in making selections. 3. Good luster of the ear is highly desirable. This means a bright, pol- ished, waxy finish regardless of color. 4. The whole ear, including the tip, should be free from all molds, weathering, and discolorations of every kind. Also the seed coats" of the kernels should not be broken, as they sometimes are, either from natural causes (Fig. 59), rough handlings, or mouse and insect activity (Fig. 61). Mouse damage may be confined to certain parts of the ear only, and if the ear is otherwise satisfactory, it may sometimes be saved by removing and discard- ing the injured kernels. 5. The butts should show a clean break of healthy tissue. Ears with shredded butts (Fig. 11), or those having yellowish or dull brownish discolora- tions, are especially to be avoided. Look for the presence of Basisporium spores (Fig. 12). 6. After the ear has been examined as a whole, a number of representa- tive kernels should be removed for examination or, if no germination test Meaning pericarp; seed coat is used here in the popular sense rather than in its exact botanical meaning. 1930] CORN DISEASES IN ILLINOIS 33 FIG. 11. ONE GOOD (LEFT) AND Two UNDESIRABLE SHANK ATTACHMENTS A clean break of healthy tissue indicates that the shank was healthy and that probably no diseases have entered the ear by that route. A rotted or shredded shank attachment indicates a probability either that diseases have entered the ear at that place or that diseases or other unfavorable circum- stances have caused the whole plant, or possibly only the shank, to die pre- maturely. The kernels of such ears are likely to carry infection, or at least may be susceptible to infection when planted. Fia. 12. BASISPORIUM SPORES AROUND THE SHANK ATTACHMENT The tiny black spores appearing here in a broken ring are the result of Basisporium infection. The majority of the kernels on such an ear are in- fected. The spores are often much more numerous than here shown. Ears with a sound shank attachment are not likely to show these fructifications. 34 BULLETIN No. 354 [September, is to be made, it is best to shell each ear individually after it has passed the tests just mentioned and then to thoroly examine the shelled kernels. There are two kinds of starch in the endosperm hard horny starch, which has an amber-like appearance in yellow corn, and soft floury starch. The difference can be noted from the exterior of the kernel (Fig. 13), the homy being semi- translucent and the floury being opaque and, in yellow corn, lighter in color. Selection should be made for a high percentage of horny starch. Ears that pass the germination test should afterwards also be shelled individually and care- fully reinspected for horniness as well as the following points: 7. The kernels should be well developed, carrying their full thickness to the point or tip of the grain (Fig. 14). FIG. 13. HORNY KERNELS OF CORN (A) ; FLOURY, OR STARCHY, KERNELS (B) In good seed the horny, amber-like endosperm should extend down to the tip of the kernel and should extend up very nearly to the cap or dent. In dent corn, floury endosperm may be a varietal characteristic or it may be an indication of immaturity of the grain. Corn kernels with a marked degree of floury endosperm are usually undesirable for seed. 8. The kernels should be free from any streaks (Fig. 15), spores (Fig. 16), and whitish, grayish or brownish discolorations. The latter are especially apt to occur toward the tip end of the kernel. 9. Cracked seed coats may occur on the sides of the kernels, where they are not noticed until the ears are shelled (Fig. 17). Such ears should be discarded. 10. When the grain is shelled from the cob, in most corn belt varieties, the tip cap of the kernel should remain on the kernel and not on the cob. These tips breaking off may or may not be a sign of disease infection, but at any rate if they break off, the grain lacks this protection and is open to infection as soon as it is planted. 1930} CORN DISEASES IN ILLINOIS FIG. 14. MATURE AND IMMATURE KERNELS IN THEIR NATURAL POSITIONS ON THE COB Mature grains carry their full thickness down to the very tip of the kernel (left). Grains that have dried and hardened while still decidedly immature (right) are not filled out at the tip, altho there may be no indication of this condition in the unshelled ear. When shelled, the undeveloped condition at the tip of the kernels, together with lack of horny endosperm in this region, is easily recognized. This lack of development may be caused by disease or by the occurrence of low temperatures before the ear is mature. FIG. 15. ONE SOUND AND THREE INFECTED KERNELS White streaks as here shown, as well as black streaks, are a good sign of fungous infection, and ears showing such a condition should not be taken for seed. A yellow or brown discoloration at the lower end of the germ is another indication of infection. By observing such signs as these and others described in the text, many undesirable ears can be eliminated from the seed lot. Even tho such ears appear free from disease in a germination test, yet field experi- ments have shown such seed to be inferior in performance. 36 BULLETIN No. 354 FIG. 16. KERNELS INFECTED WITH BASISPORIUM The tiny black spores of this fungus are observable on four of the above kernels. They are not always abundant enough, however, to be readily noticed with the naked eye (Fig. 27). Many infected kernels show no spores at all. FIG. 17. SO-CALLED "SILK CUT" OF CORN In the unshelled ear this kind of injury often is not noticeable. For the detection of this, as well as other kernel defects and discolorations, every ear should be shelled separately and the kernels carefully examined before de- ciding to use the ear for seed. 1930} CORN DISEASES IN ILLINOIS 37 Germination Test. The germination test is a good basis for judging the fitness of an ear for seed purposes. When properly con- ducted, it should indicate two important factors vigor of growth and presence or absence of certain diseases. The appearance of these diseases on the germinator is discussed later in this bulletin. Instead of the germination test being the third step in seed- corn selection, many people have made it the principal considera- tion. This the writers feel is a mistake. Plant selection and ear selection take into consideration important characters associated with the development or maintenance of disease resistance, for which the germination test cannot be substituted. Most farmers are neither equipped nor properly trained for conducting the germi- nation test most effectively. The construction and maintenance of a germinator is a problem in itself. Among other things, proper temperature, aeration, moisture of the substratum, and humidity of the atmosphere must be maintained in order to make the dis- ease symptoms or signs visible and in order to get uniform results. Altho a germination test may be necessary for best results, never- theless if plant selection, ear selection, proper curing, and seed treatment are carefully practiced, the results in a normal year seem to be nearly as satisfactory as if the germination test for the elimination of diseased ears had been added to the measures just mentioned. People who are not very careful in plant selection and ear selection will get comparatively greater returns thru selection on the germinator, if it is properly done, but the results cannot be so satisfactory, especially in the long run, as they would be if these other selections had first been made. In short, now that good seed treatments are available, physical selections (plant and ear) would ordinarily appear to be of greater importance than the germina- tion test, for resistance to certain diseases, some of them not seed borne, can be built up by physical selection while the germi- nation test, as far as disease is concerned, gives information only on seed infection, which to a considerable extent can be remedied by seed treatment. In years when, owing to damage from freezing, there is question concerning the vigor and viability of seed corn, the germination test is essential. SEED TREATMENT Successful chemical treatments for seed corn are a new develop- ment. Even five years ago there was no treatment that could be 38 BULLETIN No. 354 [September, recommended. Intensive investigations concerning the treatment of seed corn began only after organic mercury compounds had been introduced. Such a compound was used first in Germany for the control of bunt of wheat in about 1912. This compound, a chlorphe- nol-mercury, was later introduced into the United States and its application to corn in extensive field plots was probably first made in Illinois.* It gave considerable promise as compared with chemi- cals that had previously been tried. Soon a number of other organic mercury compounds of different chemical compositions were being manufactured, some good, some not so good. All these early com- pounds had decisive limitations, but manufacturing chemists had become keenly interested in the matter and more new compounds were produced. Altho most of these products were of little value, occasionally improvement was made, so that fairly reliable and effective seed disinfectants are now available. Several commercial seed disinfectants that can be recommended are on the market. These are patented materials and can be obtained only under their trade names. Other desirable and possibly superior products may be developed in the future, but of the many disinfectants so far tried, extremely few have been found to be highly desirable, and it is probable that some comparatively worthless compounds under vari- ous names will also be offered for sale to the public. On the basis of experiments thus far made it may be concluded that the average farmer of the northern or central sections of Illinois (Fig. 3) under average conditions may be fairly confident of an increase of 2 or more bushels per acre in his yield of dent corn by applying a good seed treatment at an outlay of about three cents an acre for the disinfectant. 49 - 79 * For the purpose of experi- mentation samples of corn were obtained from 285 farmers in central Illinois during the seasons 1928 and 1929. These were com- posited and grown under several different soil conditions. An aver- age increase of about 3 bushels an acre was obtained (Fig. 18) as a result of seed treatment. Under some conditions increases in stand, vigor, and yield of grain obtained from seed treatment have been very striking. Even with the very best seed obtainable, seed treatment, in Illinois ex- periments, has usually proved worth while. Ordinarily the differ- These experiments were started in 1923 by Chas. S. Reddy in cooperation with the authors of this bulletin. 1930] CORN DISEASES IN ILLINOIS 39 ence in the growth of corn from treated and untreated seed cannot readily be detected by inspection but accurate yield determinations must be made in order for the difference to be evident. Seed treatment is not, of course, a remedy against all corn diseases. The more noticeable diseases such as smut, ear rot, stalk rot, and root rot are not directly controlled by seed treatment GROWN FROM AVERAGE-FARMERS'SEED FIG. 18. DIFFERENCES IN THE VEGETATIVE GROWTH OF DENT CORN CAUSED BY SEED TREATMENT This striking difference in size occurred in 1929, when planting was fol- lowed by three weeks of cool, rainy weather. Ordinarily when fairly good seed is used, the effect of seed treatment cannot readily be detected until the husked corn is weighed. altho some may be slightly checked indirectly because of the better vigor and the more advanced development of the plants from treated seed. The best seed disinfectants now available, however, are effective in the control of many seed borne infections. This fact has to a considerable extent reduced the importance of the germination test for the control of seedling diseases. Furthermore the treatments seem to offer some protection against infection from the soil. Much of the damage to the young corn seedlings seems to be caused by the so-called "saprophytes" or "weak parasites" which occur abundantly in the soil. The predominating types of these organisms no doubt vary greatly with different soils and with dif- ferent crop sequences. When the soil is wet or cold or both, some 40 BULLETIN No. 354 [September, of the "weak parasites" are especially prone to be harmful. Under some other conditions the same organisms may be practically harm- less. Treated seed can be planted early with greater safety than untreated seed, for there is less danger of damage in case it should lie in the ground, because of unfavorable weather conditions, for a long time before sprouting. 49 * It has often been demonstrated FIG. 19. A SEED-TREATING MACHINE MADE FROM A STEEL OIL DRUM One half of one of the drum heads is cut out and a tight-fitting hinged lid is put in its place. A shaft made of one-inch iron pipe is fastened in a diagonal position thru the drum. One or several baffle boards should be fastened on the inside. This size treats one bushel of seed at a time. It is suitable for all kinds of farm seeds. that when seed of good quality from full-season varieties is used, the early-planted corn (May 1 for Urbana) usually yields the best. 69 * Altho seed treatments sometimes have proved of no bene- fit, yet in the event of unfavorable environmental conditions during the germinating period the treatments become highly beneficial and may even prevent the necessity of replanting. They have given enough return, on the average, to allow a good profit on the invest- ment. Seed treatment, it should be emphasized, is no substitute for good seed. Special attention should be given to physical selection; when well done, this is more important than seed treatment, but 1930] CORN DISEASES IN ILLINOIS 41 a good treatment may be worth while as an additional measure. In fact, farmers who have been giving careful attention to plant and ear selection for a number of years are in many cases getting more benefit from the use of a good seed disinfectant than are farmers who have spent comparatively little time in selecting their seed ears. Some of the same treatments that have proved beneficial on dent corn, when applied to sweet-corn seed, have been found to cause a substantial increase in the yield of prime canning corn. 90 - 91 * As yet no seed-treatment experiments have been conducted under the soil and climatic conditions of the southern section of the state. Claims have been made by certain manufacturers that their disinfectants not only protect the corn seedlings against dis- ease infection but that they also control insects which attack corn in the ground shortly after planting. The results of several years' tests in Illinois indicate that such is not the case. 120 * The effective commercial seed disinfectants should be applied at the rate of 1% to 2 ounces to a bushel of shelled corn by the use of a good mixing machine. Mixing the chemical dust with the grain by means of a shovel should not be attempted for three reasons: (1) a good coating of the seed cannot be obtained; (2) too much of the dust is lost in the air; and (3) the method is ex- tremely dangerous to the health of the operator. A barrel churn does very well for small quantities, but should be filled only one- third full of grain. A good mixing machine, handling a bushel at a time, can be made of a 30-gallon metal oil drum (Fig. 19). A concrete mixer answers the purpose if a tight lid can be fixed over the opening. Various commercial mixers are on the market. Care should be taken to avoid inhaling the dust. The mixing should be done out of doors or on a barn floor with the doors open on both sides. Respirators that fit over the mouth and nose so as to protect the operator are low in price and can be purchased in some drug stores. After the corn is treated it should be stored in a dry place. Leav- ing it in an open building where the humidity of the air is similar to what it is out of doors would likely be a risk under some weather conditions. Such exposure is not very apt to kill the seed but it may have a depressing effect on the vigor of the resulting crop and consequently on yields. 42 BULLETIN No. 354 [September, CAUSES OF DEAD SEED A number of diseases of corn kernels may result in death of the embryo (germ). Usually such dead kernels show external dis- colorations to the extent that they can be recognized by the man who carefully selects his seed corn. There are two diseases, how- ever, that sometimes kill without showing discolorations or other external symptoms. These are Diplodia and Gibberella. When external symptoms are lacking, infection with either of these dis- eases can be detected only by means of the germination test, which is described later in this bulletin. Other common causes of dead kernels in corn of good appearance are cold, heat, and old age. With respect to the effect of low temperatures, it is generally true that the higher the moisture of the grain the less cold it will stand without injury. Considerable difference exists, however, be- tween individual ears and individual kernels in their resistance to cold at a given moisture content. The length of time during which a low temperature is maintained is a factor also. In experiments at the Nebraska Station 64 * it was found that the danger points for seed-corn injury from exposure for 24 hours to low temperatures occurred at approximately the following moisture-temperature com- binations: 30 percent moisture, 28 F.; 25 percent moisture, 24 F.; 20 percent moisture, 16 F.; 17 percent moisture, 4 F. In any case an increase in moisture or a decrease in temperature sometimes caused considerable mortality. Somewhat lower temperatures proved safe when the time of the exposures was not so long. To just what extent these data are applicable to weather conditions in Illinois is not definitely known, but they doubtless may be taken as suggestive. On the other hand, seed may be killed by having the heat too high during the curing process. Experiments by Harrison and Wright 32 * at the Wisconsin Station have shown that ear corn dried by forced warm-air ventilation at temperatures of 104 to 113 F. was not injured. Corn dried at a temperature of 122 F. was con- siderably injured. Those investigators found that ear corn could be dried to 12 percent moisture in 72 to 96 hours at temperatures of 104 to 113 F. without injury to germination, seedling growth, or field performance. These results are in accord with experience in Illinois. 1930] CORN DISEASES IN ILLINOIS 43 Seed corn ultimately dies from old age. Under what environ- mental conditions and moisture content of grain it will live longest, and to what extent various disease infections affect longevity, have not yet been determined. It is well known that while old seed car- ried over for one year sometimes gives very good results, the vitality often is not so good after it has reached that age. The senior writer has stored nearly disease-free yellow dent seed corn of the horny type for five years, and at the end of that time found the germination perfect and vigor good. When planted in the field, the yields from such seed were very nearly the same as those from fresh seed. However, the quality of seed corn more than one year old is always to be questioned until satisfactory viability and vigor have been demonstrated by means of a germination test. It is probable that occasionally dead grains may be the result of deficient or deleterious hereditary factors. In inbred corn dead grains are frequently found that cannot be explained by causes outside the plant itself. SEEDLING DISEASES GENERAL CONSIDERATIONS There are a number of diseases of seedling corn plants that are very important. They result in poor stands, blighted plants, and weak plants. In almost any planting many grains germinate and yet do not come to the soil surface. Often this is due to a rot or blight of the seedling before it emerges. On the other hand, under field condi- tions there may be some missing plants even where only the very best seed was used, for much depends on the physical condition of the soil. The young shoot has to push its way thru to the surface or perish, and the most vigorous seedlings may be obstructed by clods that cannot be penetrated. All the diseases considered here generally cause more or less loss of vigor. As the perfection of the field stand, under any given conditions, is in proportion to the degree of vigor of the seedlings, it is evident that diseased seed is very apt to cause a poorer stand than nearly disease-free seed, even tho the disease in question does not directly cause the death of the seedlings but only reduces their vigor. 46 - 68 * Some plants blight in the seedling stage even after they have 44 BULLETIN No. 354 [September, made some growth above ground. They dry up and fall to the ground. After the first cultivation usually all trace of them is lost. Perhaps the greatest damage caused by these seedling diseases is due not to the loss in stand or blighting of plants, but rather FIG. 20. PORTION OF A CORN SEEDLING SHOWING (A) FIRST NODE, (B) SECOND NODE, (C) MESOCOTYL, (D) ADVENTITIOUS ROOTS, AND (E) SEMINAL ROOTS There is some lack of uniformity in the names applied to these parts by scientists. For instance, the seminal roots at E are sometimes called primary roots, the adventitious roots at D, secondary roots, and the mesocotyl at C, first, or subcrown, internode. to giving the young corn plant a weak start. The actual infection may extend not more than an inch away from the kernel, but it occurs at the most critical time and in the most vital place. So far as is known, the infection does not pass up the sprout farther than the crown where the adventitious roots have their origin (Fig. 20) . But as the early growth of the seedling is retarded, fewer and weaker adventitious roots are produced. Weak seedlings usually 1930} CORN DISEASES IN ILLINOIS 45 develop into plants that are handicapped thruout their life period as compared with plants from strong seedlings. 45 * Several investigators have expressed the opinion that seedling blight and consequent loss in stand is the only important harmful effect that may occur from the use of infected seed, plants that survive being just as thrifty as those grown from clean seed. On the other hand, height measurements of many plants grown from nearly disease-free seed and from seed infected with Diplodia, or TABLE 2. EFFECT OF SOME CORN SEEDLING DISEASES ON STAND AND PLANT VIGOR AS DETERMINED BY HEIGHT MEASUREMENTS OF YOUNG PLANTS (Seasons 1924 to 1927 inclusive, Urbana, Illinois) Kind of seed used Replica- tions Plants measured Average plant height Differ- ence in height number 44 number 14 452 inches 47.4 inches Infected with Diplodia zeae 44 8 352 43.3 4.1 28 7 372 40.3 Infected with Gibberella saubinetii 28 4 515 36.0 4.3 40 10 536 38.1 Susceptible to scutellum rot 40 8 980 36.1 2.0 Gibberella, or seed susceptible to scutellum rot, show that there is a difference in vigor (Table 2). Unfortunately in these tests no measurements were made on seed infected with Fusarium or Basi- sporium. It should further be borne in mind that in the case of Diplodia and Gibberella infection only about 50 percent of the surviving plants developed from infected seed, the remainder com- ing from good seed. In order to obtain seed lots of infected seed with very nearly 100 percent viability on the germinator, the per- centage of infection cannot be extremely high. The actual percent- age of infection ranged from 65 to 90 percent. The measurements shown in Table 2 were made when the plants were about waist-high, before competition for soil moisture and nutrients became a very important factor in their growth. Two kernels were planted to a hill. As shown in Table 2, the Diplodia and Gibberella infections caused considerable reduction in stand as compared with the stand from the nearly disease-free seed. The differences in stand can be obtained from the columns giving the number of plants measured. If the surviving plants from infected and non-infected seed were equally good, the yield per plant should 46 BULLETIN No. 354 [September, have been considerably better where the reduced stand occurred, be- cause of diminished competition. In fact, however, the yield per plant in the two groups was nearly equal. This also indicates that the surviving plants were weak. Losses from seedling diseases depend not only on farm prac- tices, strain of corn, and care used in its selection, but they vary also from year to year depending on climatic conditions during the maturation period. 15 * When wet weather prevails after the ears have attained maturity, so that they remain high in moisture for a considerable time, or when low temperatures kill or injure the plants before the ears are completely mature and while still high in moisture, then infected or disease-susceptible ears are unusually prevalent and the crop from such ears may suffer considerably from various seedling diseases. Concerning this Holbert and Burlison 44 * make the following statement: "Seed from cold-resistant plants has proved superior to that from plants of the same inbreds and recombinations killed prematurely by cold, even when both lots of seed apparently were equal in visible characters and in laboratory germination. This superiority of matured seed from cold-resist- ant plants expresses itself in increased seedling resistance to disease, in greater cold resistance in the fall, and in greater resistance to lodging and stalk breaking after maturity." The estimate of average annual loss in the succeeding discus- sions is based: (1) on the percentages of infection observed in numerous samples obtained from various parts of the state during a period of years; and (2) on actual losses determined in experi- mental field plots where yields from diseased seed, ranging from 65 to 90 percent infection with each respective disease, were com- pared with yields of grain obtained from the check plots planted with nearly disease-free seed, as shown in Table 3 on page 61. DIPLODIA SEEDLING DISEASE Importance. The amount of Diplodia seed infection varies con- siderably from season to season and from one location to another in the same year. Still there appears to be a certain amount of seed infected with this disease on almost every farm in Illinois in every season. Infections as high as 30 percent have been noted in what was supposed to be seed corn. The annual loss in yield of corn in the state due to Diplodia seed infection may be estimated at about 2 percent. 10801 CORN DISEASES IN ILLINOIS 47 FIG. 21. A HEALTHY SEEDLING (RIGHT) COMPARED WITH OTHER SEEDLINGS GROWN FROM DIPLODIA INFECTED SEED All four of the infected seeds germinated, but at the time the picture was taken one of the sprouts was already dead, one was dying, and another was so badly decayed at the base that it is doubtful whether it would have grown to maturity. The seedling at the right in all probability would not die as a result of seed infection, but notice the rot at the lower end of the mesocotyl and the poor vigor as compared with that of the healthy seedling. Symptoms. When Diplodia infected seed is planted, a poor stand and many weak plants are the usual result. The infection is carried within the seed. This may cause the death of the embryo (germ) so that the kernel will not sprout. Much of the infection in carefully selected seed corn, however, is not deep seated enough 48 BULLETIN No. 354 [September, to injure the embryo. In that case germination begins in the normal way when the grain is planted; but as the embryo begins to grow, the fungus also develops, and very often it overtakes the young shoot (plumule) soon after emergence from the kernel. In this case a blight resulting in the death of the plant is apt to occur. Most of the blighting occurs before the plants come thru the soil. Some plants will die even after they have made as much as six inches growth above the soil. The seminal roots also are attacked by FIG. 22. COMPARISON OF PLANTS GROWN FROM DIPLODIA INFECTED SEED AND FROM NEARLY DISEASE-FREE SEED Plantings were made at the rate of three kernels to a hill. The Diplodia infected seed produced two weak plants (left hill), while the good seed produced three strong ones (right). Photographed 44 days after planting. Compare with Fig. 23. (From Plate V, Journal of Agricultural Research.* 5 *) Diplodia. In spite of attacks on the roots or mesocotyl, some plants are not killed but struggle along and put forth some adventitious roots at the second node (Fig. 20) . After this plants of dent corn are fairly safe from blight, for the fungous invasion is usually stopped at the first node. (In sweet corn the infection sometimes ex- tends farther up the stalk. 121 *) As the mesocotyl ceases to function, the food supply from the kernel and seminal roots is cut off. This causes a great check in the vigor of the seedling (Fig. 21), and thus fewer and weaker adventitious roots are formed. Whether the majority of the infected seedlings will die or survive depends con- siderably on soil temperature and moisture as well as on the se- verity of infection and the resistance of the seedling. 1930] CORN DISEASES IN ILLINOIS 49 FIG. 23. THE SAME Two HILLS AS SHOWN IN FIG. 19 PHOTO- GRAPHED 120 DAYS AFTER PLANTING The hill on the left produced less than a pound (.84) of air-dry shelled corn and the hill on the right 2.05 pounds. Corn plants checked by disease in the seedling stage remain weak and yield poorly. (From Plate V, Journal of Agricultural Research. 4 **) Weak plants and poor stands may also be caused by other dis- eases and by insects. There are no above-ground symptoms to in- dicate whether or not the disease is caused by Diplodia. To make 50 BULLETIN No. 354 [September, a diagnosis, the seedling must be dug up and the soil carefully re- moved from the mesocotyl. A dull brown rot of the mesocotyl and a dull brown to bluish discoloration of the kernel is indicative of Diplodia infection. But if the seed coat has reddish markings in- stead of being a dull brown or slight bluish color, then the disease may be caused by Gibberella, which is the next disease described FIG. 24. TYPICAL EFFECT OF DIPLODIA SEED INFECTION ON STAND AND VIGOR OF CORN PLANTS The row of corn at the left was grown from Diplodia infected seed ; that at the right from nearly disease-free seed. Note difference in number and size of plants. herein. At times mesocotyl rots are caused by still other organisms. The weak plants caused by seedling infection remain weak thruout the season. These differences are illustrated in Figs. 22, 23, and 24. Later in the season there are no symptoms to show that the weak- ness was caused by Diplodia infection. In addition to causing loss 1930] CORN DISEASES IN ILLINOIS 51 in yield of grain, it has been found that plants grown from Diplodia infected seed are more apt to lodge than those grown from nearly disease-free seed. 68 * This condition is believed not to be caused by a rotting of the roots but to be due rather to the general weakness of the plants resulting from their having been attacked by the dis- ease in the seedling stage. The disease is most severe when the soil is relatively wet during the germinating period. 46 * Cause. The disease is caused principally by Diplodia zeae (Schw.) Lev., a fungus of the class Imperfecti. The mycelium is white when young and becomes gray when old. There is only one kind of spore. It is two-celled, dark in color, averaging 25 by 5.2 microns in size (Fig. 30). These spores are borne in pyc- nidia which are black in color. The pycnidia are borne on dead cornstalks (Fig. 46), especially near the nodes, on ear shanks, on the cobs of rotted ears, on the ra- chilla and subtending tissues at the inner ends of the kernels (Fig. 25), sometimes on the ker- nels themselves, and on the husks (Fig. 26). These dark pyc- nidia are easily seen with the naked eye. They are somewhat larger in the ear than they are on the other parts. D. macrospora Earle and D. frumenti E. and E 23, 103* h ave a j go k een re po r ted as causes of corn ear rot in the FIG. 25. CROSS-SECTION OF A DIPLODIA ROTTED EAR, NATURAL SIZE, SHOW- ING PYCNIDIA The irregularly rounded black blotches are the pycnidia, or fruiting organs, of the Diplodia fungus. Each pycnidium contains many spores so small that they are invisible to the naked eye. southeastern states. Seasonal Cycle of Parasite. Pycnidia may be produced in the fall of the year in the various parts of the corn plant mentioned above, but ordinarily most of them do not appear until the following spring and summer, especially on the stalks. During the summer, after a rain, the mature pycnidia open and the spores are liberated. These are carried by the wind to the new corn crop. The aerial 52 BULLETIN No. 354 [September, , | . > parts of normal plants are not subject to infection until the silks appear. From this time until they are too dry in the fall, the ears are subject to Diplodia in- fection. Such invasion may take place thru the silk, down the husks, thru the shank, or directly on ears not fully protected by the husks. 5 ' 36> 66 * Soon after silking, the leaf sheaths be- gin to loosen a little and then infection of leaf sheath and stalk may take place. 20 * Considerable moisture, to- gether with dead pollen and Diplodia spores, collects behind the leaf sheaths. The fungus first uses the dead pollen for food. 20 * As the fungus grows, it pro- duces enzymes which break down the delicate tissues of the axillary bud and the fungus enters the stalk there 5 * (Fig. 10). Also it may enter the stalk thru the base of the leaf sheath and thus cause nodal infec- tion. As the corn ear grows FIG. 26. DIPLODIA PYCNIDIA ox INNER HUSKS OF A ROTTED EAR These pycnidia develop on the husks and shanks, in the ear (Fig. 25), and on the stalks (Fig. 46). Unless destroyed or plowed under, the spores in these pycnidia are carried by air currents to the new crop the following year and cause infec- tion. to full size, the husks loosen and infection may occur on the ear shank just as it does on the stalk (Fig. 27) . The fungus then readily passes thru the shank to the ear. 66 * No pycnidia are formed on the ear or stalk until after these parts of the plant have died. Seed infection may cause blight or poor vigor of the resulting plant, but the fungus attack is local, beneath the soil surface, and after the infected parts of the seedling have decayed, the activity of the fungus in that region probably soon comes to an end. It has 1930] CORN DISEASES IN ILLINOIS 53 been shown that Diplodia zeae is able to grow on sterilized soil, 20 * but whether it would long be able to maintain itself in competition with the soil flora is questionable. Furthermore it is doubtful whether the fungus would fruit on soil alone. This is important, FIG. 27. DIPLODIA SHANK ROT AT AN EARLY STAGE The rot started at the base of the husk, as indicated by the arrow in A. When this husk was removed (B), a brownish rotted streak showed the path by which the fungus had reached the shank. The ear was in the milk stage of development, and when broken off from the shank, a decidedly rotted con- dition was evident at the break. By harvest time this no doubt would have been a totally rotted ear. for it appears that the following year's crop is attacked only by infection in the seed or by spores produced on corn refuse and car- ried by air currents. It is known that infected cornstalks lying on top of the soil may produce spore crops during at least two seasons. Whether the fungus will live that long on buried stalks 54 BULLETIN No. 354 [September, is not known, but it seems doubtful. If spores are produced on buried material, they cannot get into the air. Such material does not seem to infect vigorously growing corn roots (adventitious sys- tem) , even when they come in direct contact with them. If all corn refuse could be thoroly eradicated or turned under and kept under the soil surface, the disease would probably be stopped. Unfortu- nately there are obvious difficulties to such a measure. FIG. 28. DIPLODIA INFECTED EAR SHOWING ZONATION Infection began at the butt and progressed more than half way up the ear before the ear dried to the point where further growth of the fungus was in- hibited. By this time the kernels at the butt were killed. Thus on this ear there are three zones: at a the kernels are dead; at b they are infected but alive; and at c they are healthy. Infection may begin at the butt or at the tip and may extend over the whole ear. Sometimes infection has not progressed far enough to kill any of the kernels. Control. For the control of the Diplodia disease in general, in- cluding ear and stalk rots, field sanitation and crop rotation (pages 18, 19) are recommended. As yet no definite ear or plant types are known to be correlated with resistance to this disease, but it is probable that by thoro elimination of infected ears from the seed lot every year and by selection on the germinator, better resistance may be obtained. 1930] CORN DISEASES IN ILLINOIS 55 Wide variations exist in the resistance and susceptibility of inbred lines to Diplodia ear rot 41 ' 47 * (Fig. 54). In many first- generation crosses between inbreds resistant and susceptible to this disease, resistance has been dominant. Crosses between strains that have shown resistance to Diplodia rot have repeatedly had less than 1 percent of the ears damaged by this disease, while in the case of other strains, inbred and crossbred growing under the same conditions, more than 50 percent of the ears were rotted by Diplo- dia. Open-pollinated varieties also differ widely in their resistance and susceptibility to this disease. Thus, by employing sanitary .measures, by following approved crop rotations, by proper soil management, and by using strains of corn highly resistant to Diplodia ear rot, it is possible nearly to eliminate losses from this disease. The seedling blight phase can be controlled satisfactorily. Phys- ical selection of seed corn (page 32) eliminates some of the badly infected ears. On a good germinator infected kernels show well- defined symptoms, so that nearly all the infected ears can be elim- inated (page 145). Certain seed treatments (page 37) have made possible very good control of the seedling diseases in all cases in which the embryo has not been injured prior to treatment. Seed ears that appear first class frequently carry Diplodia infection. Such ears often exhibit three regions or zones, as shown in Fig. 28. The treatment cannot help zone a, which is dead, but it should stop the disease in zone b and make the kernels nearly equal to those in zone c. GIBBERELLA SEEDLING DISEASE Importance. Gibberella seedling disease causes considerable loss in some seasons, while in others it is of little and occasionally of no importance. Whether or not the seed becomes infected depends considerably on -weather conditions during the growing period of the corn ear and also on the abundance of inoculum in the atmos- phere at that time. Once the seed has become infected, more or less injury to the seedling is apt to occur from the infection unless a seed treatment is used. The average annual loss in yield due to seedling injury by this disease is estimated to be about one-half of 1 percent. Now and then losses may run up to 5 or even 7 percent. 56 BULLETIN No. 354 [September, Symptoms. Gibberella seed infection may result in very un- satisfactory stands and much seedling blight in early plantings, especially when such plantings are followed by periods of cold weather. Many infected plants that escape blight are weakened by the disease but continue growth to maturity. These usually lag GROWN FROM GOOD SEED 6MWH FROM GIBBERELLA INFECTED SEED FIG. 29. EFFECT OF GIBBERELLA SEED INFECTION ON STAND AND VIGOR OF CORN Corn grown from diseased seed makes irregular growth because of differ- ences in degree of resistance to the disease or differences in degree of infec- tion. The irregularity is further emphasized here by the fact that the diseased seed composites contained a small percentage of good seed. Note the com- paratively uniform growth in the plants grown from good, nearly disease- free seed. behind in growth, as shown in Fig. 29. When Gibberella infected seed is planted in rather warm soil, there may be little loss in stand, vigor, or yield. 14 * Such late plantings, however, even with good seed, are not conducive to high yields. The above-ground aspects of this disease are practically identical with those observed in corn grown from Diplodia infected seed. When young diseased plants are dug up carefully, the disease can frequently be dis- tinguished by the characteristic reddish discoloration of the kernel, together with a dark brown rot of the mesocotyl. Kernel infection on the ear is usually zoned similarly to the 1930] CORN DISEASES IN ILLINOIS 57 Fie. 30. SPORES OF SOME OF THE FUNGI THAT CAUSE CORN DISEASES (a) Cephalosporium acremonium ; (b) Penicillium oxalicum; (c) ascus, (d) asoospores, and (e) conidiospores of Gibberella saubinetii; (/) Ustilago zeae; (g) Diplodia zeae; (h) Aspergillus niger sp. ; (i) Rhizopus tritici; (;') macroconidia and (A) microconidia of Fu- sarium moniliforme; (1) Alternaria sp. ; (m) Physoderma zeae-maydu ; (n) Soroiporium reilianum; (o) Helminthosporium turcicum; (p) teliospores and (q) urediniospores of Puc- cinia torghi; (r) Basisporium gallarum. (Drawn with Cameralucida. All enlarged to same scale.) 58 BULLETIN No. 354 [September, situation described for Diplodia. Infection ordinarily begins at the tip end and proceeds toward the butt of the ear. Cause. This disease is caused by Gibberella saubinetii (Mont.) Sacc., a fungus of the class Ascomycetes. The mycelium varies in color from white to yellow and red. Two kinds of spores are pro- duced, conidiospores (conidia) and ascospores. The former are crescent shaped (Fig. 30) 1- to 9-septate tho usually 3- to 5-septate, and ordinarily 30 to 60 by 4.75 to 5.50 microns in size. 117 * The conidiospores when viewed in mass are light pink in color, but when viewed singly under the microscope both kinds of spores appear colorless. When planted on a suitable medium, a conidiospore may germinate and produce a mycelial growth and a new crop of conidio- spores within two days. 16 * On corn, however, the development of conidia is relatively slow and sparse. During the germination test of Gibberella infected kernels, a considerable mycelial growth often develops (Plate V) but conidiospores have seldom been observed. They also occur sparsely and sometimes not at all on Gibberella rotted ears (Plate II). On the heads of infected wheat, however, they usually are produced abundantly within three to four days after infection. The ascospores are produced within perithecia that can easily be seen with the naked eye. The perithecia can often be found in abundance on infected, old cornstalks in the spring of the year (Fig. 47). Sometimes they occur also in considerable numbers on the heads of infected wheat when the grain is mature. Within the ascus are numerous sack-like structures (asci) in each of which 8 ascospores are found. The ascospores are 1- to 3-septate, usually 3-septate, and ordinarily 20 to 30 by 3.75 to 4.25 microns in size (Fig. 30). Seasonal Cycle of Parasite. The fungus lives over winter in in- fected refuse of small grains and in infected cornstalks. Whether Gibberella rotted ears left in the field are of importance in carrying the disease over has not been determined but it is reasonable to suppose that they are. Ascospores produced on old cornstalks left on top of the ground are probably the chief source of infection for the succeeding crop. These ascospores are liberated during the growing season. If damp weather prevails for a few days imme- diately after the small grains have headed out, there may be an epidemic of scab of wheat and barley. Rye and oats also may 1930] CORN DISEASES IN ILLINOIS 59 become infected. After the silks are out, ear and stalk infection takes place in corn under suitable weather conditions. The fungus may persist for some time in infected cornstalks, or in straw and other grain refuse when it is covered with soil, but in that case the spores cannot get into the air to reinfect the new crop. Such in- fected refuse in the soil, when abundant, may be a factor in causing rot of corn roots or mesocotyl that come in contact with it, much more so than Diplodia infected refuse. To what extent the fungus is able to live in the soil apart from infected refuse is not known, but it appears to be able to do so to some extent. The fungus lives over winter in infected seed and causes the seedling disease. The attack is beneath the soil surface and the fungus does not spread very far from the kernel. When the diseased seed is held over for a year before planting, the fungus dies out and the infection is gone. All other seed infections here described that cause seedling injury are longer lived. In addition to attacking the cereals, this fungus has also been found on sweet potatoes 117 * and possibly on some other crops. Control. As in the case of Diplodia disease, if sanitation (page 18) were practiced thoroly and on an extensive scale, the disease would probably no longer be of serious consequence. This would involve not only the turning under, putting in silo, or burning of all corn refuse but also of the straw of scab-infected small grains. For the control of Gibberella corn ear infection alone, such a measure would not be practical, but as scab of small grains is con- trolled thereby and as a number of other corn diseases also are controlled by removing or plowing under corn refuse, sanitation measures no doubt are highly worth while. Altho this measure is not so effective if confined to a single farm, even in that case it is worth while and should be encouraged. A suitable system of crop rotation is also of considerable help, especially when sanitary measures cannot be carried out satisfactorily. For best disease control, corn should not be followed by corn, wheat, or barley in the rotation, for these are the crops that are most susceptible to Gibberella infection. Physical selection of seed corn (page 32) eliminates some of the very badly infected ears. The germination test (page 147) further helps in culling out infected ears. Seed treatment controls the dis- ease on kernels not too badly infected. It has been observed that 60 BULLETIN No. 354 [September, under some conditions much of the slight Gibberella seed infection will fail to become evident in the ordinary germination test made at a temperature of 75 F. or over. Yet when planted in cool soil, as usually occurs at the proper corn planting time, much injury may result. In such cases seed treatments are especially valuable as a supplement to the germination test. It has been found that various selections and strains of corn differ widely in their resistance and susceptibility to Gibberella- seedling blight. 46 ' 67 * Corn grown from seed selected according to the recommendations set forth in this bulletin has been found to be highly resistant to injury from the seedling phase of this dis- ease. 46 * And, as in the case of Diplodia ear rot, strains of corn inbred, crossbred, and open-pollinated vary greatly in their re- sistance and susceptibility to Gibberella ear rot. Some strains have been found whose ears over a period of years have been damaged only very slightly by this disease. FUSARIUM SEEDLING DISEASE Importance. Practically every seed lot in the state every year is infected with Fusarium monttijorme, and usually the percentage of infection is high, frequently running over 50 percent. Fortu- nately this fungus is not usually a vigorous pathogen; its impor- tance lies in the fact that the percentage of infection runs so high. In experimental tests in Illinois reductions have usually been observed in yields of corn grown from seed naturally infected with Fusarium moniliforme (Table 3). On the other hand, inoculating nearly disease- free seed by moistening the seed coat with a spore suspension of the organism before planting apparently did not cause infection, for it caused no decrease in yield. 46 * This is no surprise, for even with such a vigorous pathogen as Diplodia zeae, under field conditions suitable for the vigorous growth of corn in- fection usually is not obtained by inoculating the seed in the man- ner just mentioned. Investigators in several other states have ex- pressed doubt as to whether seed infection with Fusarium monili- forme is a factor in reducing yield. 25 - 77> 98 * One of these reports 98 * is based on evidence that seems to be inconclusive. Some of the in- fected seed was treated so as to kill the infection, while some of the seed was left untreated. The treated seed yielded less than the un- treated, but the treatment was a drastic one, and therefore any 1930] CORN DISEASES IN ILLINOIS 61 TABLE 3. COMPARATIVE YIELDS OF YELLOW DENT CORN GROWN FROM GOOD SEED, FROM VARIOUS KINDS OF INFECTED SEED, AND FROM SEED SUSCEPTIBLE TO SCUTELLUM ROT (Grown in various places in Illinois, 1917-1929 inclusive) Kind of seed used Years cov- ered by ex- periments Number of experi- ments Acre yield Reduction in yield following use of diseased seed Good corn Diseased corn Good 10 10 6 6 4 4 9 9 8 8 10 10 5 5 93 93 37 37 20 20 55 55 31 31 63 63 16 16 bu. 63.8 59.8 60.5 63.9 58.1 70.9 51.1 bu. 4ii5 45^6 5i!s 5s!6 54 .'4 58 .'8 49 !6 bu. 22.3 14.8 8.7 5.9 3.7 12.1 2.1 perct. 35.0 24.7 14.4 9.2 6.4 17.1 4.1 Diplodia infected Good Gibberella infected Good Basisporium infected. . . . Good Fusarium infected Good Cephalosporium infected. Good Good Scutellum rot susc. J l Seed composites selected from corn that had received no previous selection for resistance to scutellum rot. 'Altho the ears used in these seed composites showed susceptibility to scutellum rot on the germinator, they were taken from seed lots that had been bred for resistance to this disease for a number of years. benefit that might have been derived from killing the fungus very likely was more than offset by the injury caused by the treatment. It is possible, of course, that under some conditions little or no harm occurs from this infection. Differences in pathogeneity of different strains of the fungus no doubt exist. Considerable varia- tion in amount of loss has been found in different tests in Illinois, but the reasons therefor have not yet been fully explained. Soil conditions, the genetic complex of the corn, and the other environ- mental conditions no doubt are all factors in this problem. The statement made by Melchers and Johnston, 78 * "The free- dom of seed on the germinator from F. moniliforme does not seem as important in securing a satisfactory stand and yield of corn in Kansas as seedling vigor," probably also holds for Illinois. Seedling vigor is always an important consideration. Seed poor in vigor is undesirable even tho it appears to be free from infection. From data obtained in various parts of the state during the last eight years, it is estimated that the annual loss in yield due to seed infection with Fusarium moniliforme is about 1 percent. 62 BULLETIN Xo. 354 [September, Symptoms. There are no outstanding field symptoms associated with plants grown from seed infected with Fusarium monilijorme. When stands from infected seed are compared with stands from nearly disease-free seed, small reductions in stand and vigor usu- ally are found. Actual counts of the stand must be made, for ordi- nary observation does not very readily reveal it. Fusarium seed infection usually also causes a reduction in yield of grain, but here again actual weights must be taken, for no one can estimate a difference of something like 5 percent in yield without some reliable way of actually measuring it. For symptoms during the germination test, see page 141. Cause. As perithecia of this fungus have not yet been observed developing under natural conditions, the fungus is still ordinarily known as Fusarium monilijorme Sheldon. This is a species of the class Imperfecti. It produces two kinds of conidiospores, micro- conidia and macroconidia (Fig. 30) . The former are oval in shape, 2 to 3.5 by 5 to 10 microns in size. 116 * They are produced in chains (Fig. 67). In mass the conidiospores are a pale pink in color, but when viewed singly under the microscope they appear colorless. When a spore is planted under suitable conditions, a new crop of microconidia will develop in a few days. Macroconidia usually are slower in developing; these are 3- to 5-septate, and 2.9 to 3.2 by 32 to 56 microns in size. They are borne singly, not in chains. Ascospores have also been found as a spore stage of this fungus. They were observed by Wineland 116 * in cultures of the fungus isolated by the senior writer from yellow dent corn grown near Bloomington, Illinois. This puts the fungus in the Ascomycete class and therefore the name Gibberella moniliformis (Sheldon) Wineland has been given it. The perithecia resemble those of Gib- berella saubinetii and it has been suggested 116 * that they may have been seen in nature, but that they were mistaken for the better known perithecia of the latter fungus. The ascospores, however, are distinctive in appearance (Fig. 30). They are 1- to 3-septate. the 1 -septate predominating, and are 3.9 to 4.8 by 15 to 19 microns in size. There is no reason to doubt that these strains, which pro- duced the ascigerous stage in the laboratory, would also produce the same under natural conditions. On the other hand, there ap- pear to be many strains or varieties of this fungus, 74 * and from what is known so far, it seems likely that many, if not most, of CORN DISEASES IN ILLINOIS 63 these strains do not produce the ascigerous stage. It therefore seems preferable for the present to retain the Fusarium name. Seasonal Cycle o/ Parasite. Fusarium monili forme is able, ap- parently, to winter on crop refuse of various kinds. It probably does not live in the soil very long after all refuse has decayed completely. Spores developing on infected refuse exposed to the atmosphere are carried by the winds to the new corn crop. The ears become sus- ceptible to infection immediately after silking. Ordinarily most of the infected ears do not show the infection externally but the infection can be seen on the kernels during the germination test (Plate III). On infected ears, kernels with an injured seed coat, whether the injury is due to physiologic cracking (Fig. 59), worm injury, bird pecking, or other cause, usually develop this rot, es- pecially in the starchy types. Some starchy ears also develop the rot without previous seed-coat injury. The fungus is also reported as causing a blight of pine seedlings, root rot of older pines, a rot of potato tubers, a root rot of cotton, and it has been found on dead parts of banana plants. There may be other susceptible crops. Control. Good sanitation and crop rotation (pages 18, 19) would be expected to help in reducing ear infection and ear rot. Ear selection for a horny, utility type, early enough to mature well in an average season, has also been of considerable help in reducing ear rot. Strains of corn have been developed that are highly resist- ant to ear rots caused by F. moniliforme. For the control of the seedling disease caused by this fungus, careful attention to soil fertility, especially with respect to an adequate phosphorus sup- ply, 46 * is of importance. The germination test (page 141) will help in removing badly infected seed ears. Seed treatments (page 37) have proved partially effective in controlling this seedling disease. BASISPORIUM SEEDLING DISEASE Importance. The disease called "cob rot" has been known for many years, but that the fungus causing cob rot also frequently occurs in an inconspicuous way on what might be considered as seed corn has not been known very long. 22 * The prevalence of seed infection varies from year to year, heavy infection occurring when the fall is damp, especially when the dampness follows damage that resulted from the occurrence of frost while the ears were high in moisture. From the limited data available, an estimate of the aver- 64 BULLETIN No. 354 [September, age annual loss due to seed infection is difficult to make. A con- servative figure would seem to be about 1 percent (Table 3). Symptoms. The field symptoms of Basisporium resemble those observed with Gibberella and Diplodia infections. Some infected seed is dead. Some will germinate but the plants die in the seedling FIG. 31. BASISPORIUM SPORES AT THE TIP END OF A CORN KERNEL This corn kernel is enlarged 12 times. With the naked eye the presence of these spores could hardly be discerned. Sometimes the spores are so numer- ous that they are easily seen (Fig. 16), sometimes they can be detected only with hand lens or microscope, and often they do not occur at all even when the kernels carry Basisporium infection. stage. Both conditions result in a poor stand. Still other infected seedlings survive but are weakened by the infection. The disease differs from that caused by Gibberella or Diplodia, however, in that the germ of good-appearing seed that is infected with Diplodia seldom is injured prior to planting, the disease doing its damage when the kernels germinate. Basisporium, on the other hand, at- tacks the germs especially, so that even before planting, the germs of good-appearing but infected seed sometimes have been injured and will produce weak plants. This is one of the reasons why seed treatments are not always so effective with Basisporium infec- tion as they are with Gibberella and Diplodia seed infections. The symptoms that most clearly indicate infection with Basi- sporium occur on the dry ear and kernel. Infection of the ear may li)30\ CORN DISEASES IN ILLINOIS 65 occur thru the shank or tip. When it has occurred thru the shank, Basisporium spores often are visible around the shank attachment (Fig. 12). Badly infected kernels show the spores at the tip end (Fig. 16), but when infection is light, a good hand lens is necessary to see them (Fig. 31). Often the infected kernels show only a yel- lowish discoloration on the lower end of the germ portion, no spores FIG. 32. BASISPORIUM SPORES ON THE RACHILLAS As SEEN WHEN AN EAR Is BROKEN CROSSWISE When Basisporium ear rot becomes extensive in an ear, the cob breaks very easily and spores, as shown here, are numerous. Such ears usually are light and chaffy. W T hen the infection occurs late, however, the cobs are strong and no spores are visible. (Enlarged 5 times.) having developed at all, and sometimes what appear to be per- fectly good kernels carry the infection. Usually Basisporium in- fected ears are zoned. At the butt end of the ear there may be a zone in which masses of spores on the kernels are clearly evident to the naked eye (not all infected ears show spores, however), next there may be a zone in which the spores are few in number so that they can be detected only with a magnifying glass, and next to that there may be a zone in which the kernels are infected but no spores have developed. (See Fig. 28 for zoning caused by Diplodia). Cause. This seedling disease is caused by Basisporium gallarum Moll., a fungus of the class Imperfect!. The spores are black in 66 BULLETIN No. 354 [September, color, averaging 11 by 14 microns in size (Fig. 30). Altho the in- dividual spores are too small to be seen with the naked eye, they often occur in groups that can easily be seen (Fig. 16) and they sometimes occur in a solid black mass. They can be found on the protected portions of the husks, on the surface of the shanks be- neath the husks, on the inner surface of the leaf sheaths, around the shank attachment of the ear, on the surface of the cob (especial- ly on the surface of the rachilla, Fig. 32), and on the kernels. Seasonal Cycle of Parasite. The fungus overwinters in good condition on old infected cornstalks, shanks, and ears. After the ears begin to develop and the leaf sheaths and husks begin to loosen, infection of the new crop by wind-blown spores may take place. Damp weather conditions seem to be necessary in order for infection to occur. 22 * Under suitable conditions heavy infections of stalks, shanks, and ears may be found, while under some other seasonal conditions the disease is comparatively rare. It seems probable that Basisporium will not attack vigorously growing tis- sues but is able to become established only after the tissues have been reduced in vitality by disease, mechanical injury, low tem- peratures, or other cause. When a corn strain is unadapted to the soil conditions in which it is grown, or when the supply of soil nutrients is inadequate for a particular strain of corn, so that the plant does not mature normally in the fall, then high percentages of Basisporium infection are likely to be found. The same situation obtains when the corn is so constituted genetically that it does not attain full maturity before cold fall temperatures set in. There is considerable difference in resistance between different strains as well as between individual ears within an open-pollinated strain. Some strains are very sus- ceptible to Basisporium infection, even to the extent of more than 50 percent of the ears being badly damaged by this disease fol- lowing maturity and prior to harvesting, while other strains of corn, under comparable conditions, have been damaged only slightly. Resistance, no doubt, also wanes with the approach of .ma- turity. The ears of strains maturing very early are likely to be- come infected with this ear rot fungus during the warm wet weather that so frequently obtains during periods in September and October. Basisporium gallarum has also been reported as causing a fruit rot of tomato. 1930] CORN DISEASES IN ILLINOIS 67 Control. An important consideration in the control of Basi- sporium ear rot is the selection of a strain of corn capable of main- taining a physiologically balanced growth in the soil and under the prevailing climatic conditions of the place where it is grown. Corn strains that mature unusually early in the fall or, in other words, strains that dry up and die before cold weather sets in should be avoided when the crop is to be cribbed or stored. Strains utilizing the full growing season and that at the same time are capable of effecting complete maturity under the environment in which they are grown should be chosen. Ears of strains maturing too late are subject to infection following injury by low tempera- tures in October or November. Corn strains that appear to be particularly susceptible to this disease should be replaced by better strains. As for seedling infection, close attention to selection of the seed ears (page 32), with special attention to examination for the presence of the Basisporium spores (Figs. 12 and 16), is the most important consideration. A good seed treatment also has been found to be of value and should be used, for many of the lightly infected ears cannot be eliminated by the above methods. The germination test frequently is of but little help, for ordinarily no symptoms develop on the germinator that cannot be observed on the dry grain. While the moisture on the germinator does appear to make the spores more clearly visible at times, on the other hand, other fungus growths may develop which completely hide them. (For symptoms on the germinator see page 149.) SCUTELLUM ROT DISEASE Nature of the Disease. Unlike most of the other parasitic dis- eases discussed in this bulletin, scutellum rot is not caused by any one or more specific organisms; many different organisms are in- volved most of which might be classed as "weak" parasites that usually live as saprophytes. Furthermore the scutellum is by no means the only part involved. The name "scutellum rot" has been used because disease susceptibility of this type can usually be recognized by the development of scutellum rot on the germinator (page 136). For the present purpose all the effects caused by fun- gous or bacterial invasion of the endosperm or scutellum, and in- fections starting at the bases of the roots not due to other specific diseases are grouped here. Resistance to this kind of infection no 68 BULLETIN No. 354 [September, doubt is of a chemical nature. 65 * Furthermore this resistance, when it occurs, apparently is not confined to the seedling. Plants grown from seed very susceptible to scutellum rot often have been found to be more susceptible to stalk rots and ear rots than those grown from seed resistant to scutellum rot. 46 * Furthermore susceptibility to scutellum rot is correlated to a considerable degree with imma- turity. 65 * Corn from susceptible seed very often is of a plant type that will not attain complete maturity unless the season and other conditions are unusually favorable. The plants may become dry at the usual time and the ears present the superficial appearance of being mature, but being physiologically immature the full pos- sibilities of yield of grain is not attained. As the moisture content of such ears in the fall usually is greater than in fully matured ears, the hazard from ear rots in the field and in storage is con- siderably aggravated. Importance. In estimating the importance of the scutellum rot disease, the various features mentioned above must be considered. It is evident that there are seasonal variations in the importance of the disease and that there are wide variations in losses from farm to farm varying with strain of corn used, care taken in seed selection, and attention given to soil management. Considerable knowledge concerning the three factors mentioned has been at- tained and put into practice during the last ten years so that the losses from scutellum rot now are not so great as they were in the previous decade. Nevertheless the annual losses now are esti- mated to be fully 5 percent (Table 3). Symptoms. Plants grown from seed susceptible to scutellum rot usually are less vigorous than those from resistant seed. They have shorter or more-slender shoots, fewer or less-sturdy roots, and fewer laterals branching off from the first or main root. On account of impaired vigor the chances that the plant will be able to push its way up thru the soil are reduced and a decrease in stand therefore usually occurs (Table 2). When infected plants are taken from the ground and the kernels are cleaned from soil and bisected, a rot similar to that found on the germinator (Fig. 65) often can be seen. In rich well-pulverized soil there is less damage than in poor soil, for in the rich soil the young roots are able to supply nourishment sooner and the plants come thru the soil more easily. Other things being equal, the vigor of the older plants and 1930] CORN DISEASES IN ILLINOIS 69 the yield of grain are in proportion to the vigor of the young plants. 45 * (For symptoms on the germinator see page 136.) In experiments previously reported," 7 * it was demonstrated that susceptible seed (susceptible to scutellum rot on the germinator) in comparison with resistant seed produced a lower yield of grain on infested soil than it did on clean soil. It appeared that the difference was largely due to differences in the severity of root rot. It was also shown in the same publication that after the stalks had lain in the field until the following summer, there were con- siderably more perithecia of Gibberella saubinetii on the stalks grown from susceptible seed than there were on stalks grown from good seed. Thus seed susceptible to scutellum rot also appeared to TABLE 4. YIELDS AND PROPORTIONS OF UNMARKETABLE EARS FROM GOOD YEL- LOW DENT CORN AND FROM YELLOW DENT CORN SUSCEPTIBLE TO SCUTELLUM ROT, AS AFFECTED BY TIME OF PLANTING (University South Farm, Urbana, five-year average, 1921-1925) Date of planting Character of seed Acre-yield Total Sound Unmarketable May 2-4 Good bu. 66.0 53.1 65.1 54.3 62.2 50.5 58.2 46.0 bu. 57.0 42.7 55.2 43.7 53.0 39.1 47.6 : . i bu. 9.0 10.4 9.9 10.6 9.2 11.4 10.6 12.9 perct. 13.6 19.6 15.2 19.5 14.8 22.6 18.2 28.0 May 10-14 Susceptible Good May 20-22 May 30-31 Susceptible Good Susceptible Good Susceptible be more susceptible to root and stalk rot. In an article by Reddy and Holbert 89 * (Table 16 of reference) data are given showing that inoculations with C ephalosporium acremonium or Aplonobacter stewarti made into the stems of plants grown from susceptible seed (susceptible to scutellum rot) caused greater losses to yield of grain than when inoculations were made into stems of plants grown from good seed. Thus susceptibility to scutellum rot was correlated with susceptibility to stalk infection with these organisms. It was shown also, in the same table, that the inoculation of seed with Gibber- ella saubinetii at planting time was more detrimental to seed susceptible to scutellum rot than to good seed. Further data involv- ing these two types of seed also show marked differences in re- sistance to infections from seed inoculations with G. saubinetii (see pp. 423-425 of Holbert et al*) 70 BULLETIN No. 354 [September, In another publication 45 * it was shown that there was con- siderably more ear rot in corn grown from susceptible seed than in corn grown from good seed. In other tests where the ear rots were not considered specifically but the percentages of sound and unmarketable corn were determined, it was found (Table 4) that the percentages of unmarketable corn averaged higher when sus- ceptible seed was used than when good seed was used. Further- more this difference was greater in the late plantings than in the earlier planting. (See also Fig. 17 of Holbert et al. 45 *) Thus it seems evident that scutellum rot reduces the stand and vigor of plants ; and that seed susceptible to scutellum rot produces plants susceptible to Giberella seedling disease, to stalk infection by G. saubinetti, C. acremonium, and A. stewarti, and to several kinds of ear rot. Resistant seed has, on the whole, shown greater resistance to these other diseases also. Cause. Many fungi are able to cause scutellum rot. On the germinator, species of Rhizopus are usually the cause, altho Peni- cillium and Aspergillus species also cause certain types of scutellum rot at times. Under field conditions the above-mentioned fungi also are of importance but they are not the predominating ones. From corn grown in soil, species of Fusarium, Mucor, Trichoderma, and Pythium have been isolated from infected scutellum in addition to those mentioned above. Fusarium species were isolated most frequently. Penicillium species were second in frequency and Mucor species third. It has frequently been observed that losses in yield due to the use of seed susceptible to scutellum rot are greater where corn follows a previous corn crop than where no preceding corn crop had been grown for some years. 46 * Possibly this indicates that the corn becomes infected with more virulent organisms in one case than in the other. The identities of the organisms causing scutellum rot or seedling infection under different cropping systems have not been studied. Seasonal Cycle of Parasites. Probably all the parasites occurring in connection with scutellum rot live usually as saprophytes ; that is, they can grow and multiply by feeding on dead organic matter and do not need live plants for food. Their spores occur abundantly in nature in the air, and in the soil some predominating under certain conditions, others under other conditions. Most of them are 1930} CORN DISEASES IN ILLINOIS 71 LATE PLANTWo ly^ISS^Ef REE Sed 1 ^^ * (4/ . : mfo*, A .- ^ ' I FIG. 33. CORN PLANTS GROWN FROM NEARLY DISEASE-FREE SEED AND FROM SEED SUSCEPTIBLE TO SCUTELLUM ROT, PLANTED AT DIFFERENT DATES Good seed yielded best when planted early (May 1 in central Illinois), but seed susceptible to scutellum rot yielded best when planted at an interme- diate date (May 10). In any event, the yield from disease-susceptible seed was lower than that from good seed. (See also Table 4.) 72 BULLETIN No. 354 [September, not carried as internal infection of the seed, but cause infection from the outside when the kernels germinate. Penicillium and Aspergillus species are exceptions, as they are sometimes carried also within the seed. Control. Careful attention to ear selection (page 32) eliminates a large proportion of the susceptible ears. Immature kernels or those with the endosperm showing a soft, floury condition are usually especially susceptible. Not all well-matured ears, however, are highly resistant. Susceptibility varies with different ears that otherwise appear alike, and varies also to some extent with indi- vidual kernels on a single ear. For the best results, therefore, selec- tion by means of a germination test (page 136) should be made following physical selection. Eliminating ears susceptible to scutel- lum rot is important, not only because it tends to eliminate the seedling disease caused by scutellum rot, but also because corn grown from ears susceptible to scutellum rot apparently is very susceptible to root, stalk, and ear rot also, as has been pointed out. A good system of crop rotation (page 19) is of some benefit when susceptible seed is planted. Altho nearly disease-free seed yields best when planted relatively early (about May 1 for Reid Yellow Dent at Urbana), when seed susceptible to scutellum rot has to be used, best results are obtained if it is planted some ten days later (May 10). This coincides with the average corn planting time in this locality under present practices (Fig. 33). PENICILLIUM SEEDLING DISEASE Importance. As the Penicillium seedling disease has been de- scribed only recently, 53 ' 56 * no estimate of its importance under ordi- nary conditions can be made. The fact that Penicillium oxalicum has frequently been isolated from corn ears and that pure-culture seed inoculations have caused striking reductions in stand and vigor as compared with check plots grown from similar but uninoculated seed, all grown under favorable field conditions, indicates that the disease may be of considerable importance. Symptoms. Penicillium has been mentioned in the discussion of scutellum rot. The species described here, however, often invades the base of the plumule and primary root directly, rather than be- coming established first in the scutellum. From there the infection proceeds up the mesocotyl, and considerable loss in stand may re- CORN DISEASES ix ILLINOIS 73 FIG. 34. CORN SEEDLINGS GROWN FROM GOOD SEED (A), AND FROM PENICII.LIUM INFECTED SEED (B) Penicillium oxalicum causes a reduction in vigor, and in severe cases a blight of the seedlings. Notice the rot at the base of the mesocotyls. suit from blighting of the seedlings. Quoting Johann: 68 * "The first symptom of invasion by the Penicillium was the light yellow- green color of the basal half of the upper leaves. This shaded into a normal green at the tip of the leaf. As the disease progressed, the tips and margins of the leaves became dry. Eventually all the leaves became dry without a striking change in color." Many in- fected seedlings live but are stunted. This condition as well as blighting (Fig. 34) is responsible for losses to the crop, for plants 74 BULLETIN No. 354 [September, weakened by seedling diseases usually do not produce a normal yield of grain. Cause. This disease is caused by Penicillium oxaUcum Curie and Thorn (Fig. 1). It belongs to the class Imperfecti. The conidio- spores are somewhat ovoid (Fig. 30), measuring 2 by 3 to 3.5 by 5 microns in size. The fungus when fruiting appears bluish green (Plate V). When the spores are viewed singly under the micro- scope, they appear almost colorless. Seasonal Cycle of Parasite. The fungus has frequently been found on moldy corn and cornmeal and also seems to be common in soil. 11 * Its occurrence, therefore, appears to be rather general. Penicillium infection often becomes established in the corky tissues of the cap at the tip end of the kernel before the ear has become dry. Spores coming in contact with the surface of the dry kernel very likely also cause the disease. When such infected seed is planted, the fungus causes a rot of the embryo and the rot may also extend up the mesocotyl. It has been found 55 * that the cells are killed in advance of the fungus invasion, and it has been suggested that this killing of the cells is due to the diffusion of oxalic acid which is produced by the fungus. Control. Careful selection of ears for physical appearance will probably eliminate some of the more susceptible ears. Infected ears can be detected on the germinator. The value of seed treat- ment has not been determined. The pure-line method of breeding offers promise that high resistance to the disease may be attained. ASPERGILLUS SEEDLING DISEASE Altho black, yellow, green, and brown species of Aspergillus often are factors in the development of scutellum rot, some symp- toms that are distinctly different from scutellum rot have been observed by the senior author on corn seedlings grown from seed that was inoculated with certain species of Aspergillus. Inocula- tions were made with four different cultures, all being isolations from corn kernels and belonging to the following group species: one A. niger, one A. tamarii, and two A. flavus. These inoculations were made by moistening the seeds with a spore suspension of the fungus just before planting. Plantings were made in earthenware pots in the greenhouse. Each of the last three cultures mentioned produced chlorosis 1930] CORN DISEASES IN ILLINOIS 75 on the corn leaves (Fig. 35). This occurred under cool (60 F.) and warm (80 F.) temperature conditions and in several different types of soil. One of the A. flavus strains was less active in this respect than the other A. flavus and the A. tamarii. Most of the inoculated seedlings appeared perfectly white when they emerged. By the time the second leaf appeared, the tip end of the first leaf in many cases took on some green color and the plants could then be classed as FIG. 35. Two HILLS OF CORN, THE ONE AT THE RIGHT INJURED BY Aspergillus flavus Infection was produced by inoculating the kernels with a spore suspension of this fungus at planting time. This caused the greater part of the leaf surface to remain white during the early seedling stage and also caused poor vigor and blighting of some plants. virescent. 13 * As new leaves appeared they were at first white, then virescent, and finally green when the adventitious root system be- came active and the plant assumed normal characteristics. Some seedlings, however, failed to produce sufficient chlorophyl to remain alive and consequently died in about the third leaf stage. The uninoculated checks were all thrifty and normal green in color. These results were very striking when the corn was grown in the greenhouse during the winter months. The experiment was re- peated during several different seasons with similar results. But when the inoculated corn was planted in the field in May, very little evidence of virescence was noted. It seems likely that the difference in the quality of the light under these two conditions accounts for the difference in results. 76 BULLETIN No. 354 Similar inoculations made with a species of the A. niger group produced a more pronounced rot of the embryo region and meso- cotyl, so that there was a decided reduction in vigor but the plants were not virescent (Fig. 36). The mesocotyl rot was not so severe as occurs in the case of Diplodia or Gibberella infection. A. niger and A. flavus both invade the inner tissues of the mesocotyls (Fig. 37). FIG. 36. EFFECT OF SEED INOCULATION WITH Aspergillus niger ON GROWTH OF CORN SEEDLINGS Ten kernels of yellow dent corn susceptible to scutellum rot were planted in each of these pots, which were filled with virgin brown silt loam soil. The seed in the pot at the right was inoculated by moistening the kernels with a spore suspension of the fungus just before they were planted. Note reduction in stand and vigor. White sand was placed over the soil be- fore photographing in order to show the plants better. This occurs readily in the abserice of any visible external evidence of rot of these organs, the fungus gaining entrance at the base of the primary roots or thru the scutellum. Under field conditions the inoculations with A. niger caused a reduction of several bushels per acre in yield. Taubenhaus 100 * in Texas also has reported on dele- terious effects on corn seedlings due to Aspergillus species. From these investigations it appears likely that some of the Aspergilli may be factors in the reduction of seedling vigor and the production of blight aside from the role they play in the develop- ment of scutellum rot. 1930] CORN DISEASES IN ILLINOIS 77 FIG. 37. MESOCOTYLS INVADED BY Aspergillus flavus (A) AND Aspergillus niger (B) When the plants were of the size shown in Figs. 35 and 36, they were washed clean from soil, the mesocotyls were removed, surface-sterilized, washed in sterile water, and a portion removed from each end with scissors that had been flamed. Each fragment thus represents a medial section of a mesocotyl with all living organisms excluded except such as might be in the internal tissues of these fragments. Healthy internal tissues are sterile. In this case, however, these fungi had invaded the mesocotyls, and as a result of the technic here used the fungi have grown out of the ends of the frag- ments and have established colonies on the culture medium. SCLEROSPORA SEEDLING DISEASE Unlike the preceding diseases, Sclerospora seedling disease does not seem to be caused by seed infection but rather by infection from the soil. Only the young plants are susceptible. 80 * The dis- ease is caused by Sclerospora graminicola (Sacc.) Schroet. The same fungus causes a mildew on green foxtail, which is a common and troublesome weed in most cornfields. This disease has not yet been observed on corn in Illinois, but as it has been found in Iowa 80 * and Wisconsin 114 * it probably also occurs here. Infected seedlings are stunted; some die when only several inches high while others survive the attack. The diseased seedlings may show a mildew effect on the leaves, but this does not always occur. Ordinarily, Sclerospora infection on corn probably is rare. PYTHIUM SEEDLING DISEASE See Pythium root rot, page 91. 78 BULLETIN No. 354 [September, GENERAL DISEASES OF THE AERIAL PARTS BLACK BUNDLE DISEASE Importance. The black bundle disease causes considerable loss of corn. Reddy and Holbert 89 * in surveys of commercial cornfields near Bloomington, Illinois, during the years 1919, 1920, and 1921 found 6.6 percent of the plants showing typical external symptoms of this disease. Of these diseased plants 50.5 percent were barren, 19.6 percent bore only nubbins, and 29.9 percent bore ears. L. R. Te- hon and G. H. Stout, in plant disease surveys of Illinois, have ob- tained extensive data on the prevalence of the black bundle disease during the seasons 1924 to 1928." During this period they found that an average of 3.9 percent of the plants showed definite symp- toms of the disease. Most of these plants were barren or produced only small nubbins. The data also show a slight preponderance of the disease in the southern part of the state as compared with the northern region. In some fields infection of 70 percent of the plants was observed, while in some others the amount was negligible. Differences as striking as this have been observed on adjacent farms. From these surveys it would appear that the average an- nual loss in yield from the disease in Illinois is about 3 percent. Symptoms. The black bundle disease cannot be easily recog- nized until the corn is in the dough stage. In ordinary strains of corn in which the stalks normally are green, one of the outstanding symptoms of the disease is the occurrence of a reddish-purple color of the stalks and leaves. Purpling begins with the uppermost leaves and progresses downward. Usually the midrib shows coloring sooner than the rest of the blade. Very often these stalks are bar- ren or bear only nubbins. Often a number of these nubbins occur together at the same node (multiple ears), as shown in Fig. 38, and sometimes attempts at ear formation occur at an unusual num- ber of nodes (prolific ears) on plants that normally would pro- duce only one or two ears. It is not uncommon to find the infected stalks unusually large in diameter. The symptoms just mentioned are often associated, singly or in combination, with severe conditions of the disease, and they are the ones that can readily be recognized without destroying the "Unpublished data, Illinois State Natural History Survey. 1930] CORN DISEASES IN ILLINOIS 79 plant. They are not, however, an infallible guide, for the conditions just mentioned may also at times be brought on by other causes, and furthermore, not all infected plants show these symtoms. At the time the plants are approaching maturity, some of the fibro- vascular bundles in the stalks of infected plants usually show a blackened condition (Fig. 39). Many plants that appear normal outwardly and develop a large-sized ear are infected and show the black bundle condition in the interior relatively late in the season. This condition is considered the surest symptom, but the stalks have to be cut open before examination can be made and further- more there is a possibility that even this condition may at times be caused by other factors than the or- ganism here mentioned. Altho infection is sys- temic and starts in the early seedling stage, it does not seem to retard the veg- etative development of the plant. The economic loss results from the check in grain production. Cause. Black bundle FIG. 38. MULTIPLE EAR DEVELOPMENT CAUSED BY CKPHALOSPORIUM INFECTION In ordinary field corn this condition, to- gether with considerable purple discolora- tion of the stalks and leaves, indicates that the plant probably is infected with Ce- phalosporium acremonium (black bundle disease). This disease, however, does not always cause multiple ears, nor are mul- tiple ears always a sign of this disease. disease here described is caused by Cephalosporium acremonium Corda, a fun- gus of the class Imperfecti. The spores are one-celled, averaging 4.5 by 1.35 microns in size. 89 * They are borne in groups at the ends of short stalks, as illustrated 80 BULLETIN No. 354 [September, in Fig. 56. These groups or clusters of spores appear like a single spherical head under the 16-mm. objective of the microscope. Seasonal Cycle of Parasite. As many infected plants bear full- sized ears with little or no external evidence of disease, these ears, altho they actually are infected, are often used for seed ears. This FIG. 39. A HEALTHY STALK, LEFT, AND THREE OTHERS INFECTED WITH BLACK BUNDLE DISEASE The vascular bundles (strands that conduct the water and food thru the plant) are nearly white when in a healthy condition, but in advanced stages of Cephalosporium acremonium infection they become dark. This condition can be seen when the stalk is cut obliquely, as here shown. infected seed in turn is apt to produce infected plants. The in- fection passes up the vascular system of the plant. In severe cases barren plants are produced, but when the infection is light, more infected ears are again ready for harvest. It is probable that in- fection may also take place from the soil. Environmental factors are probably of considerable importance in determining seedling infection and disease development. Some- 1930] CORN DISEASES IN ILLINOIS 81 times seed especially selected for a high percentage of Cephalo- sporium infection will show relatively little of this disease in the resulting crop, while at times the best nearly disease-free seed pro- duces some plants showing symptoms of the disease. Control Measures. It is well to avoid plants with reddish- purple colorations when making plant selections (page 28) . Careful attention to the points enumerated under ear selections (page 32) is of considerable value. 46 ' 89 * To a certain extent the disease can be recognized when making the germination test (page 143) and badly diseased ears can be further discarded. However, not all in- fected ears can be avoided by these methods, especially when the selections are made on a commercial scale. Seed treatments, in the tests so far, have given only partial control of this disease. Crop rotation should be practiced. BACTERIAL WILT (Stewart's Disease) Importance. Bacterial wilt occurs on sweet, flint, flour and dent corn, but it is in sweet corn that the greatest losses occur. It is of comparatively little importance in dent corn. Early maturing varieties of sweet corn are the most susceptible. Severe losses often occur in the Golden Bantam and Cory varieties. The later varie- ties, such as Zig Zag Evergreen, Stowell's Evergreen, and Country Gentleman, have been found to be more resistant. Rand and Cash 87 * say: "An arrangement of varieties according to time of ma- turity coincides almost exactly with an arrangement according to percentage of wilt development." Where early varieties are used, half the crop is sometimes lost from attacks by this disease. Symptoms. Sweet corn plants show symptoms and are apt to die in all stages of development. Some infected plants succumb when only a few inches or a foot in height, while others live to produce good-sized ears. In young plants the leaves become limp, showing a typical wilted condition (Fig. 40). At tasseling time the tassels of infected plants often develop prematurely and are nearly white in color. 100 * Many infected plants at this time are stunted, some being only half as large as the healthy plants. A gradual dying and drying out of the leaves takes place, progressing from the base of the stem upwards. Dying occurs from the tips of the leaves downward and from the margins inward. This may occur with or without a conspicuous previous 82 BULLETIN No. 354 [September, wilting of the foliage. The rapidity with which wilting and dying take place in infected plants is in proportion to the amount of rain- fall during that period. 99 * Altho wet weather will hold back the wilt symptoms, thus allowing the infected plants to make better FIG. 40. BACTERIAL WILT OF SWEET CORN The hill at the left shows severe infection. Bacterial wilt causes great losses in the early varieties of sweet corn. It also occurs in dent corn, but is not of so much importance in that crop, and the wilted condition is not so likely to develop. (Reprinted from 111. Sta. Bui. 255.) growth, yet wet weather at the time of planting the seed tends to produce a high percentage of wilt. The surest diagnosis of bacterial wilt in sweet corn can be made by cutting across the lower part of the stem after wilting or dying symptoms are pronounced on the leaves but while the stem is 1930} CORN DISEASES IN ILLINOIS 83 still a normal green and shows no indication of collapsing. In a few minutes after the stem is cut, small droplets of the yellow bacterial slime ooze out of the vascular bundles. 104 * If the point of a pencil or other object is touched to one of these droplets and then pulled away, the slime can be stretched out some distance, forming a fine thread. In advanced cases the bundles themselves turn brown. In dent corn this ooze is not so evident, and rarely do typical wilt symptoms occur. The principal effect is a reduction in yield. Because the symptoms are not so evident, more of the disease may be present in dent corn than is ordinarily thought to be. Cause. This disease is caused by a bacterium, Aplanobacter stewarti (E.F.S.) McC. It is rod-shaped (Fig. 2, a), non-motile, yellow, and slow growing. It retains its vitality and its virulence possibly for several years; drying out causes no injury. Manner of Infection. Bacterial wilt may develop from infected seed and may also occur from bites of insects that carry the in- fection. There is experimental evidence to show that the beetle of the southern corn root worm spreads the disease when the corn is young. A little later in the season flea beetles spread the dis- ease from plant to plant. 88 * Infection directly from the soil has not yet been demonstrated. The seed may become infected in two ways: bacteria may enter by way of the cob thru the vascular system, or may ooze out of the stomata of the husks and thus besmear the kernels. This is a typical vascular disease, the bacteria being especially numerous in the vascular bundles of the infected plants. Never- theless, bacteria may also enter thru the parenchyma, as by way of the stomata, and in the later stages pockets are formed contain- ing numerous bacteria in the parenchyma, or pith, alongside the vascular elements. Control. The use of resistant, that is, late varieties of sweet corn is an important consideration where such varieties can be used to advantage. Planting in wet soil or planting late, when the soil is warm, aggravates the disease. 99 * The majority of infections in the field possibly do not come directly from the seed but are transmitted by insects. 88 * After feeding on an infected plant, in- sects carry the bacteria to other plants. Seed treatments with organic mercury compounds have not been found effective in con- trolling wilt, 90 * 84 BULLETIN No. 354 [September, Reddy and Holbert 92 * found wide variation in the resistance and susceptibility of inbred strains of dent corn to injury from artificial inoculation with the bacterial wilt organism. They expressed the belief that early strains of wilt-resistant sweet corn could be de- veloped. COMMON SMUT Importance. Common smut is well known to all corn growers and it is evident that it causes a certain amount of loss. Studies made by the Illinois State Natural History Survey 105 * during the years 1922 to 1927 show variations in the prevalence of the dis- ease from year to year. Two hundred ninety-nine fields examined during this six-year period showed 3.9 percent of the plants affected with smut galls on the stalk or ear; smut infections on leaves or tassels were not included in the figure. One-third of the 3.9 per- cent produced no ears. The other two-thirds naturally suffered more or less loss in yield. It seems evident, therefore, that the average annual loss in yield of grain during this period was at least 2 percent. Similar data for the years 1917 to 1923 107 * placed the loss in yield at 2.3 percent. Symptoms. Corn smut may occur on any of the above-ground parts of the plant. Fig. 41 illustrates smut on leaf, stalk, tassel, and ear. The leaves are the first to be attacked in any season. Next in order are tassels, ears, and stalks. The swellings are irregular and vary in size from that of a pea to a large double fist. At first these swellings are white in the interior. They are composed largely of fungus mycelium, altho corn tissue is also distributed thruout the smut gall. Later on, the white mycelium is converted into the black smut spores. The smut galls are covered with a glistening white membrane. As the smut matures, the membrane becomes thinner and thinner until it finally breaks. The millions of tiny black smut spores are then exposed and are ready to be blown about by the wind. Cause. The common corn smut is caused by Ustilago zeae, (Beckm.) Unger. This is a fungus of the class Basidiomycetes. The black spores produced in the smut gall are rough on the exterior and average 8 to 11 microns in diameter (Fig. 30). When these spores germinate, they produce only a short sprout (promycelium) microscopic in size. On this sprout a number of spores, known as sporidia or conidia, are produced. These are colorless and 1930] CORN DISEASES IN ILLINOIS 85 FIG. 41. COMMON SMUT ON LEAF (A), ON TASSEL (B), ON STALK (C) AND ON EAR (D) Common smut may occur on any of the above-ground parts of the corn plant. It attacks only corn. The spores are carried to the plant by the air; they are not seed-borne, as are the smuts of the small grains. 86 BULLETIN No. 354 [September, somewhat smaller than the black spores. This smut attacks only the corn plant. Several physiologic forms are known. 7 ' 102 * Seasonal Cycle of Parasite. The smut galls disintegrate during the late summer and autumn and the smut spores become scattered on the ground. They overwinter in soil, manure, and compost. When summer temperatures recur, together with sufficient dampness, the spores germinate and give rise to a crop of conidia. These in turn are carried by air currents to the cornfields and cause more smut infection. Only young, succulent tissue is subject to infection in the absence of wounds. Thus leaves, tassels, and ears become infected while they are in the process of development. Stalk infection takes place from spores carried behind the leaf sheath by water. From the ear on down there is a small, more-or-less rudimentary bud at each node behind each leaf sheath. This bud becomes the point of infection, and thus the stalk is invaded. This invasion reduces the sugar content of the plant, 51 * and this in turn interferes with ear development. Wounds from hail or farm implements often open the way for infection. There is some difference of opinion as to whether wet or dry weather favors the disease. Giissow and Connors 31 * state, "Dry weather holds the disease in check, but wet weather favors its rapid spread." Several previous writers have come to similar conclusions. Potter and Melchers, 85 * on the other hand, observe that corn smut is not so destructive in the humid eastern section of the United States as it is on the hot and dry plains of Kansas and Nebraska. In Illinois slightly more smut was found in the western half of the state, where there is a slightly greater summer rainfall (Fig. 5). Unlike the smuts of small grains, this smut is not seed-borne and is not systemic; that is, the disease does not start with the seedling and develop within the growing plant. Each smut gall is due to a local infection from spores carried to the plant by air currents. Seed treatment, therefore, can be of no help in control. Control. It has been demonstrated by a number of investi- gators 29 - 35> 46> 52j 53 ' 59 - 83 * that resistance and susceptibility to corn smut is inherited. This fact is important, for it offers the best op- portunity for controlling the disease even tho the situation is com- plicated by the existence of a number of physiologic forms of the fungus. 7 ' 102 * In open-pollinated corn, plant selection is the most important 1980] CORN DISEASES IN ILLINOIS 87 consideration in reducing losses from this disease. Those who have followed this practice for several years, taking seed ears only from plants that are free from smut and are desirable from the stand- point of other considerations also (page 28) are having, for the most part, very little loss from smut. Thoro protection of the ear by the husks has been shown to be of value in preventing ear in- fection. 72 * Crop rotation and sanitation also are of importance, since by such means the amount of inoculum in the cornfield may be reduced. It has been reported that spraying the plants with a fun- gicide has controlled the smut, but so far this method has been found impracticable. As stated above, seed treatment is of no help. LEAFY ABNORMALITIES OF TASSELS AND EARS Occasional fields have been found in Illinois in which some of the plants of dent corn have developed extensive leafy out- growths in place of the normal structures of tassels and ears. This has been observed in several different seasons and in widely scattered parts of the state. In a cornfield observed in Douglas county in 1927, where the field had been used as a feedlot during the previous summer, these leafy abnormalities caused a loss of at least 60 percent in yield of grain. In most cases where this dis- ease or disorder was observed, however, the actual loss in yield was comparatively slight. In a number of instances it was observed that the abnormalities occurred on the lowest part of the field. The leafy abnormalities of the tassels were in some instances nearly as large as bunches of bananas (Fig. 42). Each floret was altered so that it produced a structure which superficially appeared like a young corn plant (Fig. 43). Very often the plants with such transformed tassels also exhibited a leafy branch in place of an ear, in some extreme cases the leafy branch being so extensive that the end touched the ground. A great deal of common smut was fre- quently found on the tender foliage of these abnormal growths. The cause of this disorder has not been determined. Apparently Sorosporium reilianum sometimes causes leafy outgrowths of this sort instead of the spore masses known as head smut. 12 ' 93 * In some fields where these leafy abnormalities were observed in Illinois, a careful search for head smut was made but none was found. A number of Sclerospora species have been reported to be the cause of leafy malformations of the floral organs of maize, teosinte, and BULLETIN No. 354 [September, other graminaceous hosts. 115 * Some rare cases of apogamy (de- velopment of new plants nonsexually from parts that normally pro- duce sex organs) have been observed in maize plants, presumably in FIG. 42. LEAFY ABNORMALITY OF THE CORN TASSEL A large mass of leafy growth has developed in place of the normal tassel. The cause of this abnormality as observed in Illinois has not been determined. the absence of disease. 9 * It is well known, furthermore, that there are many heritable abnormalities in corn, but apparently this par- ticular abnormality is not caused by heritable factors. 1930] CORN DISEASES IN ILLINOIS 89 FIG. 43. PORTIONS OF AN ABNORMAL TASSEL SUCH AS SHOWN IN FIG. 42 In place of the normal floral organs, much larger vegetative growths re- sembling young corn plants have formed. The cross lines are one inch apart. ROOT ROTS GENERAL CONSIDERATIONS In the earlier investigations the seedling diseases just described were classed under the general term "root rot." It was known that many plants are afflicted with a root rot thruout their life period (Fig. 44) but the cause had not been investigated, and even now the information on root rot of older plants is meager. It is becom- ing evident, however, that rots due to seed infection are confined to an area rather close to the seed, and that the more widespread root rot is not caused by seed infection but rather by organisms oc- curring in the soil. It is well to make a distinction, therefore, be- 90 BULLETIN No. 354 [September, tween seedling diseases and a rot that involves the major part of the root system. It seems apparent from the data obtained in one of the field tests that the plowing under of a badly scabbed crop of spring wheat caused a considerable decrease in the yield of the following FIG. 44. SUSCEPTIBILITY AND RESISTANCE TO ROOT ROT Portions of two root systems, the one on the left having been damaged by root rot and the other showing practically no injury. (Reprinted from 111. Sta. Bui. 255.) corn crop. 67 * There is evidence to indicate that only the seminal root system, together with the mesocotyl, is susceptible to Gibber- ella infection, not only when infection is carried on the seed but also when infection occurs from the presence of the fungus in the soil. This conception does not change the economic significance of soil infestation with Gibberella saubinetii, but does help consider- ably toward an understanding of the root rot situation. Recently a Pythium root rot has been described by several in- vestigators. 3 - 57 - lia * This causes a rot of the cauline root system. 1930} CORN DISEASES IN ILLINOIS 91 The discovery has thrown considerable light on the corn root rot problem. Whether there are still other organisms that are able to cause an extensive root rot under good soil conditions remains to be determined. PYTHIUM ROOT ROT Importance. A Pythium fungus has been identified as causing root rot in Kentucky, 111 * Missouri, 3 * and Wisconsin. 57 * There is a great deal of root rot all over Illinois. This is most evident at the time the ears have reached the dent stage. Tests made with a specially designed pulling machine 48 * showed variations of 5 pounds to 700 pounds in the resistance of corn plants to a vertical stress which pulled them out of the ground. Such differences can be found in many fields. To a considerable extent these differences in root anchorage are due to differences in the natural development of the root system, but another very important factor in producing these variations would appear to be root rot. Many of the plants that pulled up easily were severely afflicted with root rot. Injuries due to such rot are severe and very extensive in the state, causing a general loss of at least 5 percent in yield of grain and probably considerably more. To what extent this loss in Illinois is due to Pythium has not been determined. It can only be said that so far, in soil of well- balanced fertility, Pythium is the only fungus that has been defi- nitely determined as causing a rot of the adventitious root system, and it has been isolated from rotted roots collected in several parts of the state. Symptoms. Quoting Johann, Holbert, and Dickson: 57 * "Pyth- ium injury to corn may be manifest as (1) a rot of the embryo, preventing germination; (2) as a seedling blight after emergence; or (3) as a root rot that tends to reduce the size, vigor, and yield of the maturing plant." It was found that germination may be prevented by attack of the fungus at low temperatures 54 to 60 F. particularly in wet soils; also that when growth takes place, a soft rot of the seedling root system may develop. "In such plants subsequent invasion of the mesocotyl occurs and seedling blight results. Or, a mild root rot may occur, not severe enough to kill the seedling, yet resulting in a reduction in size and vigor, due to the decreased root surface and perhaps to the effect of toxins produced in the invaded cortical areas." Pythium does not commonly attack the mesocotyl and in that 92 BULLETIN No. 354 [September, respect is unlike Diplodia and Gibberella. Altho the roots may be severely rotted, the mesocotyl usually remains sound. The fine- branching rootlets are the first to be attacked, and from those parts the fungus travels inward to the large roots. In digging up plants, the infected parts are easily broken off and left behind, so that the presence of the fungus may be difficult to determine. Valleau, Karruker, and Johnson 111 * state: "About the time of ear formation in Kentucky, it is difficult, on corn grown in some long-cultivated fields, to find more than a few live roots, the plants appearing to subsist on moisture and plant food drawn from the soil largely thru dead roots and new roots thrown out after rainy periods." From their experiments they conclude that this rot is caused by a species of Pythium. Branstetter 3 * in Missouri found that evidences of corn root rot do not appear until about the time of ear formation. He says, "At this stage the roots begin to rot badly, so that in a short time a fully developed stalk may be rather easily lifted out of the soil, all of the main roots being rotted off at the depth of three or four inches." He found this condition rather general in Missouri. He also found Pythium in the rotted roots and concluded that the rot was probably caused primarily by this fungus. Cause. Pythium root rot is caused by Pythium arrhenomanes Drech., a fungus of the class Phycomycetes. It produces oogonia, antheridia, conidia, and sporangia. The oogonium (female cell) is fertilized by an antheridium (male cell) and the result is a heavy walled oospore. These oospores often are found in diseased corn roots. They measure 20 to 30 microns in diameter. The conidia are somewhat similar in appearance but are produced without fertiliza- tion. The sporangia produce numerous zoospores which are able to swim about in water. They are short lived. Some other Pythium species may also be involved. 26 * Life Cycle of Parasite. The species of Pythium causing corn root rot appears to be a parasite that lives only in the soil. It is not carried on the seed. It was found that the same species that affect corn also attack the roots of sugar cane, sorghum, wheat, and oats, but legumes are not affected by them. 26 * Control Measures. Crop rotation (page 19) seems to be of con- siderable importance in holding the disease in check. There also is strong indication that some strains are more resistant than 1930} CORN DISEASES IN ILLINOIS 93 others. 57 * Plant selection (page 28) , with good care to picking ears only from well-rooted, apparently sound plants, should therefore tend toward more general resistance to the disease. Information on the relation of water drainage and nutritional factors to the de- velopment of the disease is needed. MALNUTRITIONAL ROOT ROT In many localities in Illinois a severe condition of root rot and sometimes a stalk rot has been observed. These areas often are limited to a few acres in size altho in some cases much larger regions are involved. In most instances the application of potash salts or coarse manures has remedied the situation. The plants usually start growth fairly well. In severe cases growth may be checked when waist-high. Owing to root rot, and sometimes stalk rot, many plants fall to the ground during August. In less-severe cases the plants may grow to full size but the ears fail to develop and fill out properly. It was concluded by Sears 97 * that the abnormal growth of corn on these soils is due, not to a single condition, but to a combination of factors, chief among which is a lack of avail- able potassium in combination with a concentration of nitrate nitro- gen, which is harmful. This conclusion is based on the assumption that a favorable physiological balance is desirable, particularly with reference to potassium and nitrate nitrogen. Under unbalanced nutritional conditions of the soil, Hoffer and Carr 39 * and Hoffer and Trost 40 * found that iron and aluminum compounds accumulated in the cornstalks. They state that these accumulations are toxic to the plants and render the roots especially susceptible to the development of root rot. They found that defi- ciencies of lime, phosphate, and potassium were especially prone to cause these disturbances. They also found that there was a genetic difference in individual plants in resistance and susceptibility to metal accumulations and the accompanying root rot. In a later article by Hoffer 38 * directions for making chemical tests to de- termine plant- food needs were given. In a number of fields in southern Illinois in 1928 and 1929, where unusually severe root rot took place so that the plants were decidedly underdeveloped and many had fallen to the ground, chemical tests of the stalks were made by the senior writer. These tests showed an excess of nitrates in the internodes, together with heavy iron deposits at the nodes. This would indicate a potassium 94 BULLETIN No. 354 [September, deficiency according to the Hoffer test. In a field adjacent to one of these badly diseased fields, where the corn was tall and standing up well, the stalks gave a similar test. Here too the corn may have been suffering to some extent from metal poisoning, but certainly not to the extent that occurred in the badly diseased field. It was found that no sweet-clover crop had been turned under in this ad- jacent field, and therefore it evidently was not so rich in nitrogen and consequently not so much out of balance, altho the stalks showed an excess of nitrates and iron accumulation. The chemical test alone does not seem to be precise enough to predict the degree of mineral deficiency of the soil, but the general appearance of the plant must also be taken into consideration. This observation is in accordance with statements made by Hoffer. 38 * STALK ROTS BACTERIAL STALK ROT Importance. Illinois appears to be near the northern limit for the development of bacterial stalk rot. Only rarely has it been found to cause an appreciable loss in any fields in the state. In Arkansas, however, it was found to be at times the most destruc- tive disease of corn, losses as high as 30 percent having been observed. 96 * So far the disease has not been found in the northern part of Illinois, McLean and Hancock counties being the northern- most counties in which it has been observed. Moist, warm weather is necessary for the development of this disease. In addition to occurring on field corn, the disease has also been found on Golden Bantam, StowelPs Evergreen, and Country Gentleman sweet corn. Symptoms. Infection takes place in young as well as in older plants. The rot occurs at the lower nodes and in advanced stages may readily cause the stalks to fall over. Infection passes up and down the stalk to a very limited extent only. At times the rot involves the outer circumference of the stalk, causing a dark soft decay there (Fig. 45) , while at other times the rotted area is prin- cipally in the interior of the stalk, so that only a shell remains. In either case the stalk is apt to fall. Most of the infections usually escape notice because they are not so severe, involving only a small area of the diameter of the stalk. In addition to the rotting of the stalk a light to dark-brown rotting of the leaf sheath may take place, the rot usually beginning in the parts that join the stem. 1930] CORN DISEASES IN ILLINOIS 95 After such a rot has developed, the blades of these leaves may become yellow and die. Cause. The disease is caused by a rod-shaped non-motile bac- terium (Fig. 2, a) named Phytomonas (Pseudomonas) dissolvens FIG. 45. BACTERIAL STALK ROT OF CORN This disease occurs in local areas on the lower portion of the cornstalk. When infection is severe, the stalk is very apt to fall. (Courtesy H. R. Rosen, Arkansas Agricultural Experiment Station.) Rosen. It is somewhat sensitive to drying, freezing, and sunlight. Growth in culture is fairly rapid. The colonies are white in color. Seasonal Cycle of Parasite. Just how the infection is first intro- duced into a field, how the bacteria are able to live thru the winter, and how long they may remain alive in the soil or corn refuse and be able to cause new infections has not been determined. Rosen 96 * has made the suggestion that the bacteria may possibly be carried on the seed and also that they may overwinter in the bases of 96 BULLETIN No. 354 [September, the old corn plants. Even if the corn is cut off, much of the in- fected material would remain in the field because the disease very often occurs close to the soil level of the stalk. Infection of the new crop takes place readily only when the weather is very damp and when the temperature is 85 F. or over. So far, this bacterium has been found to be pathogenic only on corn. Infections may take place thru stomata, insect injuries, and cracks in the stalks occur- ring where the brace roots push thru. 96 * Control. As the disease is ordinarily of no economic impor- tance in Illinois, no attention to control measures has been given. Crop rotation (see page 19) is probably the best recommendation wherever the disease is of consequence. DIPLODIA STALK ROT Importance. By the time the corn is in the dent stage, many stalks may be infected with Diplodia zeae. Most of these stalks are green. This rot accounts for many of the broken stalks, the amount of breaking depending in part on the severity of the winds. This breaking of the stalks often allows the ears to rest on the ground, where they may rot. Husking them is made difficult. Even where no breaking occurs, a considerable rotting of the stalk would check food translocation and therefore hinder the full development of the ear. By the last part of September a considerable number of dead stalks may be noticed in the fields with numerous Diplodia pycnidia scattered over the lower nodes (Fig. 46). Whether such stalks were killed by the stalk infection, or whether they died from other causes, is not clear. The dying plants are easily invaded by Diplodia, the pycnidia of which may be found on most pieces of old cornstalks in the fields in the spring or summer. In addition, many of the shanks are attacked. A considerable number of these break, thus inhibiting the final maturing processes of the ear. It is evident from the foregoing that Diplodia stalk rot is a real eco- nomic factor, but in the absence of carefully controlled experiments to determine this loss, and as many of the losses are indirect, it is almost impossible to make a percentage estimate that would mean anything. It may be said, however, that the loss in yield due to Diplodia and other stalk rots is at least 2 percent. Symptoms. Practically no Diplodia stalk rot takes place until the tassels are full-sized and ear development has begun. Up to 1930] CORN DISEASES IN ILLINOIS 97 this time the leaf sheaths have clasped the stems very closely, but now growth in size of the plant (excepting the ear) practically ceases and the leaf sheaths begin to loosen. Infection of the stalk FIG. 46. DIPLODIA PYCNIDIA ON DEAD CORNSTALKS The larger part of each pycnidium is buried in the tissue, only the point coming to the surface. These Pycnidia can be found in the fall on plants that have died early, but on other stalks they are not so apt to develop until the following season. Each pycnidium contains many spores, which are dispersed by the air when mature and reinfect the next corn crop. occurs in the moist region within the leaf sheath and has been observed to occur largely thru the axillary bud (Fig. 10) and thru the tissues of the leaf sheaths as they become continuous with the stalk tissues. By the end of August rotted areas can usually be found by splitting open the lower four or five nodes of the stalks. 98 BULLETIN No. 354 [September, A month later these areas are much more extensive, extending some distance up and down from the nodes. The rot is brown in color. This browning also appears on the exterior of the stalk. Sometimes the rots originating at consecutive nodes overlap in the internode, but rarely does the rot starting at one node progress thru the inter- node until it involves the next node, except at the base of the stalk and in the shank, where the nodes are very close together. Pyc- nidia are not produced until the affected part of the plant is dead. These rots are responsible for many broken shanks and fallen stalks. 21 * When Diplodia inoculum is present, this kind of stalk rot may be worse when the plants are grown on soil having a high level of productivity than on less-productive soil. The use of corn selec- tions resistant to this rot is the most effective means of control. In strains having high resistance and planted on well-managed soil, there should be little or no trouble from Diplodia stalk rot. For cause, seasonal cycle, and further discussion of control, see page 51. OTHER STALK ROTS AND INJURIES In addition to finding Diplodia as a common cause of stalk rot, Gibberella saubinetii, Basisporium gallarum, and a Fusarium species have frequently been isolated from the infected nodes of cornstalks by Durrell 21 * in Iowa. Apparently all these fungi have a pronounced effect in reducing the breaking strength of the stalks. The common ear rot fungus Fusarium moniliforme seems not to have been found in the infected corn nodes used in DurrelPs ex- periment, but Gibberella was abundant in his isolations made in 1923. Judging from the prevalence of Gibberella perithecia on old cornstalks left out in the field over winter and examined the next summer (Fig. 47), the extent of Gibberella stalk infection varies widely from season to season. This is in accordance with the wide seasonal variations in severity of Gibberella ear rot and the scab of small grains. It has been reported that brown spot infection of the stalks, especially at the nodes, sometimes is the cause of considerable stalk breaking in Kansas. 58 * Stalk breaking from this cause has not been observed to any marked degree in Illinois. Hoffer and Carr 39 * state that "in a large majority of cases the common Fusarium moniliforme Shel., Gibberella saubinetii (Mont.) 1930] CORN DISEASES IN ILLINOIS Sacc., Penicillium sp., Rhizopus sp., an unidentified white bacteri- um, and others are found to be present, especially if the nodal tis- sues in the lower parts of the stalk are cultured." They also found, however, that in many cases no organism could be isolated from brownish-purple, discolored nodal tissues. They concluded that this discoloration may often result from an accumulation of iron and aluminum compounds in the stalk due to unbalanced soil nutritional FlG. 47. GlBBERELLA PERITHECIA ON AN OLD CORNSTALK Unlike the Diplodia fruiting bodies (Fig. 46), these perithecia are not im- bedded in the stalk but occur on the outside of it. In some seasons these are very common at wheat-heading time on old cornstalks left lying on the ground' over winter. The spores are carried by the air and infect the small grains and corn when the weather conditions are favorable for infection to take place. conditions. They also concluded that infection with the organisms they mentioned may possibly be limited to cornstalks previously injured or predisposed to infection by the iron or aluminum com- pounds. Porter, 84 * in making isolations from cornstalks collected over an area of 20 different states, found that the most prevalent fungi isolated from the nodes occurred in the following descending order: Mucor spp., Fusarium spp., Fusarium moniliforme, Penicillium spp.,. Rhizopus nigricans, Aspergillus niger group, yeasts, Alternaria spp., Diplodia zeae. All these organisms occurred in more than 1 percent of the isolations; others occurred less frequently. In addition, sev- eral types of bacteria were frequently found. Porter concluded that most of these organisms are purely saprophytic, entering the nodes- 100 BULLETIN No. 354 [September, only after they have previously been killed by accumulations of toxic metallic compounds due to faulty nutritional conditions. It seems to be a fact that under some circumstances nodes or stalks die prematurely as a result of toxic conditions, and after death the tissues are easily entered by saprophytic organisms. On the other hand, many immature green stalks without internal nodal discolorations are infected at one or several nodes. It does not seem likely that this condition could obtain without the action of a para- sitic organism. The experience of the writers has been that when nodal discol- orations are caused by faulty nutrition (metal accumulation), all the lower nodes are more or less uniformly discolored and the dis- coloration in each node is fairly uniform in cross-section. Fungus infections or rots, on the other hand, in the absence of the abnormal physiologic discolorations just mentioned, occur irregularly on the stalks. One or several nodes may be badly discolored while others appear healthy. Furthermore, one side of a node may be badly discolored, the rot extending several inches up and down the stalk, while little rot may occur on the opposite side of the node, the rot being very irregular in cross-sections of the stalk. Another kind of stalk injury that is now receiving attention is caused by low temperatures. 42 ' 43> 44 * Death of the leaves, altho sometimes a vital factor, is not of so much significance as death of the stalk. When the stalk dies, translocation of food stops, and unless the ear is mature at the time, it must remain immature. The ear will dry out and will sometimes present the superficial appear- ance of maturity, but a close inspection is likely to show that it lacks luster, is not as horny as it should be, the kernels are not fully developed at the tip end (Fig. 14), and that it possesses other characteristics associated with immaturity, such as susceptibility to certain diseases. Such ears are lighter in weight and thus the yield is reduced. In more extreme cases the ears are chaffy. 41 * Stalks and shanks that are killed by low temperatures while in an immature, sappy condition are quickly overrun and pene- trated by various saprophytic organisms. 44 * The breaking strength of the stalks is thus reduced and such corn is very apt to go down. Organisms entering the shank are apt to enter the ear also. The temperature need not be down to freezing to cause injury. Quoting from Holbert and Burlison: 44 * "Some strains are injured by a succession of cool nights during which the temperature drops 1930} CORN DISEASES IN ILLINOIS 101 only to 50 or 40 F. Other strains are killed by a few hours of exposure to temperatures around 40. Altho some strains may not actually be killed by such temperatures, their maturing often may be slowed down sufficiently to reduce the quality of the grain. Corn from plants killed prematurely by cold not only is inferior in quality but also is more susceptible to ear rots." It is stated also that some recombinations of inbred strains apparently were not injured by exposure to a temperature of 28 F. for several hours, and that open-pollinated varieties have been improved in their re- sistance to cold by continuous selection toward that goal. LEAF DISEASES AND DEFECTS RUST Importance. Ordinarily corn rust causes only very slight in- jury to dent corn, but occasionally heavy infections have been ob- served, especially on certain strains. In one investigation 113 * it was found that sweet corn was the most susceptible. Next in order were flint, flour, dent, and pop corn, the latter being the most resistant. It is known also that there are considerable differences in resistance and susceptibility within strains of these subspecies. Symptoms. Rusty spots develop on the leaf blades (Fig. 48). These first appear as small, elongated blisters. The epidermis over these blisters soon breaks and the brown spores are taken up by air currents and are spread to other plants. As the epidermis breaks, the spots (sori) become rather irregular in outline. In the summer the sori are rusty brown in color, but later in the fall as the winter spores (teliospores) develop, these sori become nearly black. Rust will hardly be confused with any other disease except "brown spot," which is described next. Cause. This rust is caused by Puccinia sorghi Schw., a fungus of the class Basidiomycetes. It has four spore forms. The pycnio- spores and aeciospores are found only on certain species of Oxalis (wood sorrel, lady's sorrel, etc.) while the urediniospores and telio- spores (Fig. 30) are found only on corn. The urediniospores are dark brown in color, one-celled, nearly spherical, and measure 23 to 30 by 22 to 26 microns in size. The teliospores are a very dark brown, usually are two-celled, and measure 28 to 45 by 12 to 17 microns. The stalks on which the teliospores are borne often stay 102 BULLETIN No. 354 [September, with the spores when they become detached. Several physiologic forms of the rust are known. 75 ' 102 * Seasonal Cycle of Parasite. This rust in some respects is simi- lar to the black stem rust of small grains. The two stages on Oxalis correspond to those on the barberry, and the two stages on the corn FIG. 48. CORN RUST ON LEAF BLADES In summer the spots of corn rust are rusty brown. The epidermis breaks open as the spores mature, and in the fall the spots become nearly black. This rust is distinct from the rusts of the small grains, and so does not cross over from one crop to the other. (Courtesy E. B. Mains, U. S. Dept. of Agriculture and Purdue University Agricultural Experiment Station.) plant correspond to those on the small grains. The pycniospores of the corn rust fungus doubtless function in initiating the produc- tion of aeciospores, which are borne on Oxalis. This conclusion is based on the recent discovery of the function of the pycniospores of black stem rust of small grains. The aeciospores, borne on Oxalis, are able to infect only corn plants. After the corn becomes infected, the rusty brown urediniospores are produced. These also are able to infect corn only and serve to spread the disease in the cornfields. Late in the season the very dark-colored teliospores are formed. 1930] CORN DISEASES IN ILLINOIS 103 These cannot infect the corn, but in the spring they germinate on the old leaves on the ground and produce another crop of spores, the sporidia. These infect only Oxalis, and thus the cycle is com- pleted. In rusts, the teliospores are the typical overwintering spores, while the urediniospores are produced in large numbers in the sum- mer and serve to spread the disease, but they are not so hardy and usually do not overwinter well in northern climates. To what extent the rust on corn is first started in the season by overwintered urediniospores from the previous corn crop or by aeciospores from Oxalis has not been determined. Some pathologists, because they could not find infected Oxalis, have assumed that it is caused primarily by overwintered urediniospores. It has been shown, how- ever, in some experiments that in Wisconsin 113 * and Iowa 101 * uredi- niospores do not remain alive overwinter, and it has been observed that sometimes aeciospores can be found rather readily on Oxalis. Control. Altho rust ordinarily does not cause any commercial loss in dent corn in Illinois, the writers have observed a few com- mercial fields in which there was considerable injury to the leaves and probably a reduction in yield as a result of rust infection. In developing inbred and crossbred strains of corn, individual plants, progenies, and occasional crosses may occur that are very susceptible to rust. Other plants and progenies, on the other hand, are practically free from rust infection in the same field under the same conditions. The selection and breeding of strains of corn highly resistant to rust is the most effective method for the control of this disease. BROWN SPOT Importance. Brown spot causes considerable loss in the south- ern states, but becomes of less importance northward. Northern Illinois is about the northern limit of its distribution. Only rarely has the disease been found to be of importance in this state. All varieties of corn, including sweet and pop corn, are susceptible. 110 * Symptoms. The disease can be recognized by the circular brown blisters produced on leaf blades, leaf sheaths (Fig. 49), and stalks. It occurs primarily on the lower half of the plant. In Illinois the blisters have been observed principally on the inner surface of the leaf sheaths, on the lower portion of the blades, and on the nodes 104 BULLETIN No. 354 [September, of the stalk. Infected sheaths are more or less discolored but care must be taken not to confuse this disease with the purple sheath disease described on page 105. On the blades these brown spots are sometimes taken for rust, but the rust spots are more irregular in shape and occur on the upper blades as abundantly as on the lower. Furthermore the rust spots are more evenly distributed over the leaf surface and the rust pustules break the leaf surface conspicu- ously while those of the brown spot do not. Occasionally brown spot may be the cause of considerable stalk breaking. 58 * FIG. 49. BROWN SPOT ON A LEAF SHEATH AND A LEAF BLADE These spots are brown in color but they are more rounded than those caused by rust. They occur mostly on the leaf sheath (A) and lower end of the blade (B) and are covered by the epidermis as long as the plant is green. Cause. Brown spot is caused by Physoderma zeae-maydis Shaw, a fungus of the class Chytridiales. The brown dust in the dark spots on the plant consists of many spore-like bodies which are zoosporangia. These are 18 to 24 by 20 to 30 microns in size and are dark brown in color. They resemble the urediniospores of corn rust somewhat. The zoosporangium is somewhat flattened on one side and this place is provided with a sort of lid. On germination this lid opens and a number of swarm spores come forth. These swim about rapidly for a time in the film of water which is neces- sary for germination. Seasonal Cycle of Parasite. The zoosporangia overwinter in the 1930] CORN DISEASES IN ILLINOIS 105 corn refuse or soil, and in the following year they are carried to the new corn crop by wind, insects, water, or other agencies. After they have come in contact with the young corn plants, plenty of moisture and warm weather are necessary in order for them to germinate. After the swarm spores are liberated, they swim about for a while, then settle down on the host epidermis and produce a mycelium which penetrates the epidermis and thus causes in- fection. Germination does not take place at temperatures lower than 73 F. 110 * In addition to occurring on the various kinds of corn, this disease also occurs on teosinte. Control. Occasionally a few inbred strains have been heavily infected with the brown spot disease in this state. But always there have been in contiguous rows other inbreds on which no evidence of the disease could be found. In case brown spot ever does become of economic importance in Illinois, undoubtedly resistant strains will be available or can be developed for the section in which they are needed. PURPLE SHEATH SPOT Importance. Altho the purple sheath spot disease occurs on nearly every corn plant grown under practical farming conditions, the actual damage done by it seems to be small. Symptoms. A purplish, reddish, or brownish discoloration oc- curs on the leaf sheath after pollinating time. Typical cases are shown in Fig. 50. Altho the outer surface of the sheaths clearly shows this discoloration, the epidermis is smooth and intact. But when the leaf sheath is broken loose, it is seen that the inner sur- face presents a more-or-less corroded appearance. Ordinarily no fungus growth or fruiting bodies are noticeable with the naked eye. Where the sheaths are invaded by Diplodia, death of the infected portion often ensues and the spot or blotch then becomes a grayish color. 19 * Cause. Most of this spotting is caused by so-called saprophy- tic organisms fungi and bacteria. 19 * A considerable number are involved. This clearly demonstrates again that the term "sapro- phyte" is only a relative one, many of the organisms so named becoming parasitic only when conditions become favorable enough for the organism or unfavorable enough for the host. Diplodia a typical parasite, also is responsible for such spots. 106 BULLETIN No. 354 [September, FIG. 50. PURPLE SHEATH SPOT DISEASE The purple blotching characteristic of this disease is very common and is sometimes confused with the symptoms produced by "brown spot." These sheaths were from above the ear, but the disease may be even more severe on sheaths below the ear. Manner of Infection. While the stalks are growing, the leaf sheaths clasp the stalk tightly and the inner surfaces of the sheaths are clean. At pollinating time, growth in height ceases and the leaf sheaths loosen, so that dead pollen falls behind the leaf sheaths, together with spores, dust, and organisms of various kinds. Im- 1930] CORN DISEASES IN ILLINOIS 107 portant also is the fact that moisture accumulates in this region, so that ordinarily it is damp. Various organisms begin growth, first living saprophytically on the dead pollen, and apparently as they make vigorous saprophytic growth, enzymes are produced which work on the inner surface of the sheath, so that a collapse of the tissue takes place. Most of these organisms are not able to attack the stalk; Diplodia, however, is able to do so (see page 96). Control. Wide variations in resistance and susceptibility to the purple sheath spot disease exist, not only in inbred and crossbred strains, but also to a lesser extent in open-pollinated strains. While some strains are very susceptible, almost every leaf sheath being badly affected, other strains are only very slightly affected. Selec- tion and breeding for resistance to this disease has been found effective. HELMINTHOSPORIUM LEAF BLIGHT Importance. Usually leaf blight is of little importance, for under average Illinois conditions it attacks the leaves only after they are waning in vitality. Under certain weather conditions, how- ever, the younger plants may be attacked and considerable loss result. Such a condition has been reported from the Atlantic coast region, where, in an unusual year, this disease caused the leaves in August and September to appear as tho they had been killed by frost. No such severe damage has as yet been noted in Illinois. The disease is common on sweet corn as well as on dent corn. Symptoms. The disease ordinarily becomes evident by the first of September as elongated, straw-colored, dry blotches, especially on the lower leaves. At first these blotches are small, half an inch or less in length, but they enlarge rapidly. Several weeks later a large portion of each infected leaf may be involved (Fig. 51). By the time the blotches are several inches in length, it is stated by Drechsler, 17 * "a grayish, greenish efflorescence makes its appear- ance in the center of the withered area, becoming gradually more extensive with the continued enlargement of the latter. This efflorescence consists of the numerous fructifications of the fungus which .... are more readily perceived with the naked eye than the fructifications of the majority of the species of Helmintho- sporium developing on the foliage of grasses." This blight should not be confused with other types of "firing" due to genetic, nutritional, or moisture factors. 108 BULLETIN No. 354 [September, Cause. Corn leaf blight is caused by Helminthosporium tur- cicum Pass., a fungus of the class Imperfecti. By examining with a microscope the efflorescence appearing on the withered spots, it is seen that this consists of conidiophores and conidia, the conidio- phores appearing in groups of 2 to 6 thru the openings of the stoma- ta. 17 * The conidia are 1- to 8-septate, greenish to brownish yellow in color, and measure 45 to 132 by 15 to 25 microns in size. FIG. 51. HELMINTHOSPORIUM LEAF BLIGHT These blotches are typical after the corn has reached the dent stage. The dark centers of the blotches are composed of the fruiting structures of the fungus. Ordinarily the disease doea not become prominent until late in the season and it therefore causes only slight injury. Seasonal Cycle of Parasite. Nothing is definitely known concern- ing the form or manner in which the fungus remains alive during the winter. It is assumed, however, that it overwinters on the old crop refuse, and that in the following season the spores are carried by wind or other agencies to the new corn crop. In addition to at- tacking corn, the disease also occurs on sorghum and probably on some grasses. Control. Altho this disease ordinarily is of relatively little im- portance in Illinois, general control measures discussed earlier in this bulletin should help to reduce its prevalence. 1930] CORN DISEASES IN ILLINOIS 109 HOLCUS BACTERIAL SPOT Importance. Holcus bacterial spot seems to be of little im- portance on corn, altho it causes some injury to sorghum, sudan grass, and broom corn. Symptoms. The spots appearing with this disease are circular, elliptical, and irregular in shape, usually not more than one-fourth inch in width. The center of the spot becomes light to medium brown in color and this region is surrounded by a darker border, reddish to dark brown on corn, but bright red on sorghum and sudan grass. On corn these spots have been observed principally on the lower leaves, and usually are more numerous towards the tip end. Infections have been noticed as early as the last week of June. 61 * Cause. This disease is caused by a bacterium, Bacterium hold Kendrick. It is rod-shaped, has polar flagella (Fig. 2), is not readily killed by freezing or drying, but will not grow at a tem- perature above 95 F. 61 * The death point is higher. Seasonal Cycle of Parasite. Indications are that the bacteria causing this disease are carried in or on the seed of sorghum, and that they probably also overwinter in the soil. It is believed that the infection is not carried on seed corn, but that the corn crop becomes infected either from bacteria in the soil or from infections on sorghum or other infected grasses. Wet weather favors infection. Control. Sanitation, crop rotation, and breeding for resistance (pages 18 to 37) are recommended. The effect of seed treatment in eliminating the infection on sorghum seed has not been investigated. LEAF FIRING Most types of leaf firing become noticeable after the pollinating period, but certain types may occur even sooner. Often the upper leaves are affected principally, sometimes only the lower leaves, and sometimes the outer ends or the margins of all the leaves are dead. Firing may be fairly general in a field or only certain plants show distinct symptoms. In the former case the trouble may be due to lack of moisture or plant-food materials or to unbalanced nutri- tional conditions. A lack of potash or nitrogen in the soil is especi- ally prone to cause firing. When only certain plants show firing, the trouble probably is due to disease infection or to heritable weak- nesses in the functional capacities of the plant. A heritable defect 110 BULLETIN No. 354 [September, sometimes called "top firing" is very striking. The upper leaves, as well as the tassel, die shortly after the tassel has emerged. This, as well as some other types of firing, may occur when an abundant supply of soil moisture and plant food is available. Proper soil man- agement and careful selection of plants should in time tend to reduce greatly the number of plants susceptible to these disorders. Another type of firing is caused by sun scald during excessively hot weather. This may occur while there is an abundant supply of soil moisture, but is hastened by drouthy conditions. HERITABLE CHLOROPHYL DEFICIENCIES There are a number of leaf spots and streaks which, in some cases, resemble diseased conditions but which in reality are herit- able deficiencies. A considerable number of such deficiencies, the expression of which is controlled by separate genetic factors, have been described, but only a few that occur frequently in open-pol- linated corn will be mentioned here. Such chlorophyl deficiencies can be found in ordinary open-pollinated corn. Striped Leaves. At corn cultivating time or when going thru the cornfield later, once in a great while one may see a plant with striped leaves, the stripes being continuous and uniform thruout the length of the leaf. On second glance it will be noted that all the leaves of the plant are striped in the same manner. Such plants will occasionally be found even tho one has been very careful to pick the seed only from apparently normal, healthy plants. A number of distinctly different kinds of stripings are known and spe- cific names have been assigned to them. There are wide stripes and narrow stripes and variations in color; normal green alternat- ing with light green stripes, green alternating with yellow and green with white. Some plants are striped beginning with the first seed- ling leaf. Sometimes the seedlings appear normal in color and the stripes make their appearance one or two months later. Spotted Leaves. Spotted leaves occur somewhat more frequent- ly than striped leaves. A common type is shown in Fig. 52, B tho the spots may be either considerably larger or smaller than there shown. This defect has also been called "blotch leaf." 27 * The spots or blotches are yellow in color. They may be circular, oval, or irregular in outline. Sometimes they appear very like those caused by parasitic organisms on some other plants. They appear 1930} CORN DISEASES IN ILLINOIS 111 only after the plant has attained some size and then they develop rather suddenly on all the leaves of the affected plant. Dying Between the Veins. This defect is distinct from the other two defects just mentioned. It makes its appearance later in the season, after pollinating time, and is more pronounced on the upper part of the plant than on the lower part. It occurs as disjointed stripes bounded by the leaf veins (Fig. 52, A}. The tissue in these FIG. 52. Two TYPES OF HEREDITARY DEFECTS IN CORN LEAVES (A) "Dying between the veins." These streaks appear after tasseling time and are most prominent on the upper half of the plant. (B) "Spotted leaf." This defect is rather uniform on all the leaves of the affected plant, and the tissue of the affected spots does not die so quickly as in A. stripes soon dies, becoming straw colored, and later this dead tissue is apt to break, thus causing the leaf to appear riddled. Rapid dying of the abnormal tissue is not characteristic of the striped or spotted leaves previously discussed. Corn leaves that show the condition known as "dying between the veins" have been found to contain considerably more aluminum and iron than normal leaves. 37 * It seems, therefore, that this defect is an expression of a certain abnormal nutritional reaction within the plant which, in turn, is governed by heredity and possibly by soil conditions. 112 BULLETIN No. 354 [September, ROLLED LEAVES When passing thru nearly any cornfield one can observe, at or before tasseling time, some plants with the upper leaves tightly rolled together (Fig. 53). Often the color of the rolled leaves is lighter green than normal. This is another inherited defect. In some types the symptoms are most pronounced on highly productive FIG. 53. ROLLED TOP, A HERITABLE DEFECT This defect can be observed in most cornfields planted with open-pol- linated strains. soil. Sometimes it is impossible to unroll the leaves without tearing them, but in most instances the tassel finally pushes thru, and later these plants frequently cannot be distinguished from normal plants. No doubt there are a number of distinctly different types of rolled leaves. One type was described by Carver 6 * as "rolled" and another type was called by Kempton 60 * "adherent." The 1930} CORN DISEASES IN ILLINOIS 113 "rolled top" condition shown in Fig. 53 very likely is different from either one of the two just mentioned. Control of Inherited Defects. Careful attention to the charac- teristics of the parent plant ("Plant Selection," page 28) when selecting the seed ears usually keeps the visible heritable defects down to a small percentage. Another method that promises to be more effective has been investigated by Woodworth, Winter, and Mumm. They self-pollinate many plants in a good, adapted strain of corn, and then plant part of each "selfed" ear in a performance test. The remnants of the desirable ears are then shelled and mixed. "The variety is thus reconstituted, as the self-fertilization elimi- nates considerable defective germ plasm and also weak, low-yield- ing types, thus leaving only the best material that was present in the variety at the start." 118 * EAR ROTS AND OTHER EAR DEFECTS GENERAL CONSIDERATIONS Ear rots occur in practically every field and in every season, but there are great differences in the amount of damage done by them. Certain factors responsible for these differences, such as sanitation, crop rotation, soil fertility, seed selection, and strain of corn, are under the control of the farmer. Another important factor, the weather, cannot be controlled. On experiment fields of the Illi- nois Station it has been observed, for instance, that a strain of Northwestern Dent was particularly susceptible to Diplodia ear rot altho relatively resistant to Fusarium ear rot. The more "starchy" corn types are, as a rule, the most susceptible to the latter rot. The use of strains resistant to rots is a very important factor in control. Infections in the seed that is planted, however, has little or no direct influence on the amount of ear rot that will take place. 70 * In general, damp weather is favorable for ear rot. Losses stated in this section as due to the ear rots described are based on data obtained by the senior writer from three rotation systems on the Experiment Station farm at Urbana over a period of six years, 1924 to 1929. Nearly all the corn was harvested and the separations were made during the month of November. The total loss from ear rot during this period was approximately 7% percent. Good, adapted strains of Reid Yellow Dent were used in these tests, and it is believed that the farming practices followed 114 BULLETIN No. 354 [September, probably were better than the average in the state. At this figure, the annual loss due to ear rot in the state as a whole is about 23 million bushels. But as most farmers pay less attention to sanita- tion and grow corn that has had less selection for disease resistance, the actual loss in the state probably is greater than this figure. Furthermore these figures indicate only the loss at harvest time and do not take into consideration the additional losses that may occur in the crib. Some of the ear injuries caused by insects, mice, or defective heredity discussed in this section are indirectly related to disease. Corn so injured is more subject to certain infections when used for seed, and furthermore is more apt to deteriorate in storage than is uninjured grain, owing to activities of microorganisms when suffi- cient moisture is present. Only the better known ear rots are discussed here; still other types are to be found, especially in frosted corn. DIPLODIA EAR ROT Importance. Further investigations have substantiated the find- ings of Burrill and Barrett 5 * in 1909 that Diplodia ear rot ordi- narily is the most serious corn ear rot in Illinois. When examining the ears in the fall of the year, Diplodia ear rot can be found in almost any field, but considerable variation in severity does occur as a result of differences in farm practices and weather conditions and to differences in the strains of corn used. Differences in resistance and susceptibility to the disease exist in both open-pollinated and inbred strains 46 ' 4T * (Fig. 54) . The average annual loss from Diplodia ear rot on the plots above referred to was found to be about 3% percent. Considerable in- crease in percentage of Diplodia ear rot has been observed on No- vember 1 as compared with October 1. This agrees with data ob- tained in Ohio. 8 * Ear rot data, to be reliable, must therefore be ob- tained late in the season. Similarly, a farmer is likely to find less ear rot if he harvests his corn early, but the rots will probably continue to develop in the crib, so that the final result may be worse than if the corn had been left longer in the field. But when the ears can be dried promptly, harvesting immediately after ma- turity reduces the loss. Here also is a good argument for harvesting and drying seed corn as soon as it is fully mature. As this fungus is active at a relatively low moisture content of 19301 CORN DISEASES IN ILLINOIS 115 the corn, down to about 22 percent, considerable additional loss may occur during mild weather after the corn is cribbed. Not only will the rot spread from rotted ears to adjacent sound ones, but many ears at harvest time carry the infection altho no rot has as yet developed at that time. Symptoms. When infection takes place at pollinating time or in the milk stage, the infected ear becomes a shrunken, light-weight A-PESISTANT Sound ^Diplodia-Rotted FIG. 54. CORN STRAINS DIFFER WIDELY IN THEIR RESISTANCE TO EAR ROTS Inbred line A has consistently shown marked resistance to Diplodia ear rot, while line B has proved very susceptible. Wide differences in resistance to Fusarium, Gibberella, and Basisporium ear rot have likewise been found in inbred lines. Differences in resistance to several of the ear rots have also been observed in open-pollinated strains. mummy. The poorly developed rotted kernels are a dull brown in color and the grayish-white mycelium occupies the spaces between the kernels. This condition is illustrated in Plate II, ear G. Such mummies break very easily. Late in the fall, pycnidia can often be found when such ears are broken (Fig. 25). The husks are tight on these ears, for the fungus has grown thru them and joined them tightly to the ear. As the ears develop past the milk stage, they may become infected from either the tip or the butt end, butt infections usually predominating. Altho the ears now are larger, they still may become totally worthless, like ear E, Plate II. Infection apparently started at the tip end of this eg a d o> 13 J C o3 < 4A 3 0) 45 tc i 45 b o> s S 3 2 c i 2 .a jQ "o eS ^ '* :: S 05 Bs, n '43 0) a 93 0) o 1 02 40' C 1 88 O 4) .O ~ o ' 00 "9 c -o (5 03 O "o ~ *4 ! -o "G TJ c fa "d 'S o3 T3 c O CU S "c 1 fl} c -1 eg S !-, o -fj -u O 03 u 0) V g. rt 3 -c (I) O "G , ; 08 ni fa . -*J i fa Fusarium *=' C S 3 -t- .co .g Diplodia 1 B H JQ 1 g , O Q & "* 3 fa OS O 0) 45 Q