U. S. DEPARTMENT OF AGRICULTURE OFFICE OF EXPERIMENT STATIONS— FARMERS' INSTITUTE LECTURE NO. 2 (Rev.). A. C. TRUE, Director. SYLLABUS OF ILLUSTRATED LECTURE ON POTATO DISEASES AND THEIR TREATMENT. BY F. C. STEWART, M. S., and H. J. EUSTACE, B. S., Agricultural Experiment Station, Geneva, N. Y. WASHINGTON: GOVERNMENT PRINTING OFFICE. 1907. 736 U. S. DEPARTMENT OF AGRICULTURE OFFICE OF EXPERIMENT STATIONS-FARMERS' INSTITUTE LECTURE NO. 2 (Rev.). A. C. TRUE, Director. SYLLABUS OF ILLUSTRATED LECTURE ON POTATO DISEASES AND THEIR TREATMENT. BY F. C. STEWART, M. S., and H. J. EUSTACE. B. S., Agricultural Experiment Station, Geneva, N. Y. WASHINGTON: GOVERNMENT PRINTING OFFICE. 1907. PREFATORY NOTE. This syllabus of a lecture upon Potato Diseases and Their Treat- ment, by F. C. Stewart, M. S., Botanist, and II. J, Eustace, B. S., Assistant Botanist, of the New York Agricultural Experiment Station, Geneva, N. Y., is accompanied by 47 views illustrating methods for controlling potato diseases. The syllabus and views have been pre- pared for the purpose of aiding farmers' institute lecturers in their presentation of this subject before institute audiences. The numbers in the margins of the pages of the syllabus refer to similar numbers on the lantern slides and to their legends as given in the Appendix; those in the body of the text refer to corresponding numbers in the list of authorities and references, page 29. In order that those using the lecture may have opportunity to fully acquaint themselves with the subject, references to its recent literature are given in the Appendix. John Hamilton, Farmers* Institute Specialist. Recommended for publication. A. C. True, Director. Publication authorized. James Wilson, Secretary of Agriculture. Washington, D. C, October i, 190b. (2) POTATO DISEASES AND THEIR TREATMENT. By F. C. Stewart, M. 8., and H. J. Eustace, B. S. INTRODUCTION. View. For the most part farmers recognize but three potato dis- eases, namely, blight, rot, and scab. The first important fact to be stated is that there are several kinds of potato blight, and treatment which prevents one kind of blight may be entirely worthless for another kind. Likewise, there are different kinds of potato rot. Unfortunately, these blights and rots are often difficult to distinguish without the aid of a microscope. Farmers can scarcely expect to be able always to identify them with certainty, but it is worth while to learn the leading symptoms of the principal diseases in order that rational methods of treatment may be employed. Doubtful cases may be referred to the State experiment station. PRINCIPAL DISEASES. Early Blight. la — A widespread disease, probably more ^ destructive in the aggregate than late blight. Attacks chiefly the leaves, sometimes also the stems, but never the tubers. Appears in the form of dead, brown spots irregularly distrib- uted over the leaf, but most numerous around the margins and in portions mutilated by insects. The larger spots show concentric rings often described as " target-board" markings. Spots frequently coalesce and form large areas of dead tissue. 2 In the later stages the dry tips and margins of the leaves may roll up as in tip burn. Disease ma}^ appear at any time after the plants are 6 inches high, the older leaves being attacked first. The virulence of the disease increases with the age of the plants. Because of its slow progress it is regarded by many farmers as the natural ripening of the plants. Probably it often reduces the yield by as much as 25 to 50 bushels per « Numbers refer to list of references on p. 29. (3) acre without attracting attention. Plants suffering from drought, insufficient food, flea-beetle attack, or any thing else tending to reduce their rigor, are especially liable to attack. Early blight is caused by the parasitic fungus AUernaria solani. It may he largely prevented by spraying with Bordeaux mix- ture. Tii- Hi i:\. A common trouble often confused with early blight The tips and margins of the have- dry, blacken, and roll up. Spots with "target-board" markings also may occur on interior of old leaves. Disease most troublesome as plant- approach maturity. Caused primarily by dry, hot weather and lack of water in the soil. Aggravated by attacks of insects, particularly flea-beetles, the punctures of which greatly increase the loss of water from the leaves; also by injury to the roots through too deep cultivation late in the season. Potatoes grown on light, sandy soil are especially liable to tip burn. With regard to the prevention of tip burn. Prof. L. H. Jones, an authority on the subject, say-: Effort should be made to increase and sustain the general vigor of the plant by proper selection of varieties, preparation and cultivation of the soil, and protection against the attacks of insects and fungi. The only thing that can be done in addition is to irrigate in times of extreme drought. * * * In the Eastern States proper attention to the accumulation of a store of humus in the soil by the more frequent growth of clover, etc., will do much to reduce injuries from tip burn. Such preparation of the soil, with more frequent tillage during periods of drought, and proper spraying with Bordeaux mixture, will reduce the damage to a thing of little practical importance. Sun Scald.* — Sun scald is considered by some pathologists as a form of tip burn. When a long period of cloudy, wet weather is immediately followed by several hot, bright days, potato foliage may be injured by sun scald. The tips and mar- gins of the younger leaves suddenly turn brown and dry up as in tip burn. Leaves grown in cloudy, damp weather are tender, and too readily lose their water by evaporation when exposed to the sun. The extent of the damage done by sun scald is uncertain, but it is probably not great. Its symptoms are so similar to those of tip burn that it is impossible to distinguish the two diseases except in the early stages and when the weather conditions are known. Paris-green Injury. 5 — Paris green is now quite generally used on potatoes to prevent the ravages of the Colorado potato beetle and other insects which feed on the foliage. When properly applied with limewater or Bordeaux mixture View. and in moderate amount (8 ounces to 1 pound in 50 gallons of water), it is entirely harmless to potato foliage. But it is an undeniable fact that its use by farmers frequently results in considerable damage. Many cases of supposed blight are nothing but Paris-green injury. The symptoms of Paris-green injury are very similar to those of early blight. Dead brown spots appear on the leaves. Even the target markings are sometimes seen. Injury is most likely to occur where the tissue has been mutilated by insects, as, for example, around flea-beetle punctures. Leaves with unbroken epidermis are not 1 often affected. Paris green, as found on the market, varies somewhat in chemical composition. 6 Its poisoning properties are mainly due to the arsenic it contains. Most of the arsenic is in the form of compounds insoluble in water, but there is almost always present a small amount of soluble arsenic compounds. It is the water-soluble arsenic that causes injury to foliage, and the less there is of it the better. In some States this is regulated by law. In New York legal Paris green must not contain more than 3£ per cent of soluble arsenic compounds. The remedy for this trouble lies in the use of an equal quan- tity of lime with the Paris green. With lime the soluble arsenic forms insoluble arsenite of lime which is harmless to foliage. When Paris green is used with Bordeaux mixture the lime in the Bordeaux neutralizes the soluble arsenic, and injury to the foliage is thus prevented. To insure safety Paris green should be used only with limewater or with Bor- deaux. If used in dry form air-slaked lime should be mixed with it. London purple and other arsenical poisons containing water- soluble arsenic compounds produce injury similar to that made by Paris green, and should invariably be applied with lime- water or Bordeaux. It should also be stated that many farmers use Paris green in excessive amount. This is not only wasteful, but the dan- ger of injury to the foliage is unnecessarily increased. One pound per acre evenl}< distributed is entirely sufficient to con- trol Colorado potato beetles, or "bugs" as they are called. 7 Late Blight and Rot. 8 — This form of blight makes its appearance during warm, moist ("muggy ") weather in August and September. It may occur on earlypotatoes in Jul}', but it is chiefly destructive to late potatoes during the last month of their growth. Hence the name late blight. It tir-t appears od the leaves (usually the lower ones) in the 5 form of BmaU In-own spots which rapidly enlarge. On the under surface the margins of the diseased spots are covered with a tine frost-like mildew. In moist, cloudy weather this mildew i- easily seen, hut on a dry day it may be difficult to detect. Affected Leaves soon die. Under favorable condi- tions the disease progresses with astonishing rapidity. A tine field of potatoes may he completely ruined in a few day- after <> the first appearance of the disease. Plants in the advanced stage of the disease have onlv small tufts of green leai the tips of the stalk-. Afostof the leave- hang blackened and shriveled as if scorched by lire. Blighted fields emit a strong odor, particularly when the foliage i- wet. Contrary to popular opinion this blight is not caused by 7 wet weather. The real cause is a parasitic fungus, PhytopK- thora infegtans. Without the fungus there could be no blight of this kind, no matter what the weather might be. Blight is most virulent in wet weather simply because the blight fun- gus thrives best and spreads most rapidly in wet weather. The frost-like mildew on the under surface of the diseased spots is composed of minute, branching, tree-like affairs. These are the spore-stalks of the fungus. At the end of branch there is a minute egg-shaped body — a spore. When a spore falls upon a healthy potato leaf in a drop of water it germinates in a few hours and forces a slender, colorless thread into the tissue of the leaf. Once within the leaf the colorless thread branches many times and penetrates the leaf in all directions, absorbing nourishment from the cells of the leaf and later killing them. As the leaf tissue dies the fungus forms spore-stalks bearing new spores, and the life cycle is complete. Usually four or rive days elapse between the germ- ination of the spores and the production of a new crop of spores. Hence the rapidity with which the disease spreads. 8 Late blight may or may not be followed by rot of the tubers, according to soil and weather conditions. Rot is worse in wet, heavy soils (clay and loam) than in sandy soil. When rot occurs it is due to -pores from the blighted plants, which fall upon the ground and are washed down to the tubers by rain. Sometimes the fungus passes down the stem to the tubers, but this method of infection is the exception rather than the rule. The potato blight has no spores which live over winter. It is believed to pass the winter in the tissue of slightly affected View. tubers. Hence the inadvisability of planting tubers showing signs of rot. 9 In America late blight is destructive chiefly in the north- eastern United States and Canada. In the South and West it is not common. It is estimated that in New York the loss from late blight in 1903 amounted to 50 bushels per acre on the average. 10 In Vermont the loss is often much greater than this. 11 The virulence of the disease varies much from year to year with the weather conditions, always being great- est in wet seasons. Late blight may be prevented by thor- ough and frequent spraying with Bordeaux mixture. Bacterial Wilt and Wet Rot. 12 — Characterized by a 9 sudden wilting of the plants, followed by a wet rot of the tubers. Caused by bacteria {Bacillus solanacearum). Infec- tion probably occurs both above and below ground. Spread largely by leaf-eating insects. Same disease attacks tomatoes and egg plants. Destructive chiefly in the South. The ex- tent of its ravages in the North is uncertain, but probably considerable. The rot caused by it is often confused with that caused try the late-blight fungus. Dry Rot. 13 — Attacks all parts of the plant below ground — 10 tubers, tuber stems, roots, and lower portion of the stem. The first indication of trouble is seen in the curling and roll- ing of the leaves, which at the same time become paler green than normal. This symptom may occur at any time after the plants are a foot high. It is followed by gradual drying up and premature death of the plant. When first dug the tubers of affected plants appear sound, and are often marketed with- out the disease being detected. But when cut across at the H stem end there is seen a ring of black or brown streaks ex- tending from the stem into the flesh. This is the most reliable symptom. Hence disease is sometimes called bundle black- ening. So long as they are in the ground the tubers do not rot, but in storage the blackening of the tissue increases and ultimately many of the tubers become shriveled up with dry rot. Frequently one end of the tuber is dry rotten while the other end remains sound. Because of this peculiarity the disease is often called dry end-rot. 12 The cause of dry rot is a fungus (Fusarium oxyspmtim), the 13 feeding threads of which occur abundantly in the diseased tissue of stem, roots, and tubers, being especially conspicuous in spring on the rotten tubers, where it appears in the form of dense, whitish tufts breaking through the skin. 8 Vieu Dry rot seems to be common throughout the United States, but it has been bo much confused with other forms of blight and rot that the amount of damage done by it is difficult to estimate. J 4 & ah." — Found only on the tubers; never attacks the tops; almost too well known to need description. The skin of the tulxM- becomes roughened, pitted, and cracked in various Ways. A widespread and destructive (Usee During the past fifty year- scab ha- been studied by many investigators, and many theories as to it> cause have been advanced. 11 It is now believed that scab may he due to dif- ferent causes, hut that by far the greater part of the trouble in this country is caused by a parasitic fungus (Oospora scabies). The scab ulcers often become a lodging place for various species of fungi and insects, which feed upon the dead tissue and in some cases extend the injury. Our knowledge of the true nature of potato scab rests chiefly upon the investigations in 1890 of Dr. R. Thaxter w at the Connecticut Experiment Station. He discovered the fungus Oospora scabies, and by artificially inoculating glow- ing tubers with pure cultures of it proved it to be the cause 15 of scab. In one case he applied some of the fungus to the surface of a tuber in the form of his monogram. "R, T." This was done without injury to the skin, and yet in about three weeks scab appeared wherever the fungus had been applied and nowhere else. The scab fungus lives from year to year in the soil. It is spread chiefly by means of diseased tubers used for seed. Iry the washing of soil, and on tools used in cultivation: also in 16 manure from animals fed on scabby potatoes. The beet often sutlers from scab caused by the same fungus, and it is suspected that the turnip and some other plants are occasion- ally attacked by it. 17 Rhizoctonia, 18 Rosette, and "Little Potatoes." — Rhizoctonia is a fungus often found on the underground parts of various plants. In some cases it i- parasitic and destructive: for example, stem rot of carnation, rot of green- house lettuce, and root rot of beets. In many other cases it appears to be but little if at all injurious to the plants infested by it. There are different kinds or species of Rhizoctonia. but how many is not known. The one infesting the carnation is the same as that on the beet, but different from the one on lettuce. In Europe Rhizoctonia solani is believed to cause a rot of potato tubers. In the United 9 View. States a species of Rhizoetonia occurs abundantly on potato tubers and stems. In appearance it is very similar to the European R. sola?ii, but it does not rot the tubers and is not often seriously injurious to the plants in any way. This is our opinion. Some other plant pathologists think differently. It is apparently the cause of a serious disease in the South, and in the Middle and Western States, but does little harm in the Northeastern States. Selby, 19 of Ohio, has described a prevalent disease of 17 potatoes in that State which he calls "rosette." It is charac- terized by stunted growth, clustering of the leaves in rosettes, and premature death of the plants. He attributes the trouble to Rhizoetonia. Rolfs, 20 of Colorado, believes Rhizoetonia to be one of the principal causes of failure with potatoes in some parts of Colorado. He says it attacks the tuber stems, also girdles the main stem underground, thereby causing the develop- ment of an abnormally large top and a cluster of small potatoes at the surface of the soil. This trouble is known as "little potatoes." On the tubers, Rhizoetonia forms compact brown bodies 18 called sclerotia. They are irregular in outline and vary in size from a mere speck to the size of a half pea. When dry they are dirt-colored and difficult to detect, but when wet thej are dark brown and easily seen. They adhere firmly and are difficult to remove by washing. Many housekeepers are familiar with them. The feeding threads (hypha?) found 19 on potato stems are rather coarser than is usual with fungi, nearly colorless when young, but brown when old. The sclerotia are composed of short, thick, brown cells, closely packed together. Internal Browning. 31 — Occasional^ found in various parts of the United States, but not an important disease. Out- wardly the tubers appear sound, but when cut disclose numer- ous irregular rust-brown spots scattered through the flesh. Although affected tubers do not rot they are unfit for table use. Both cause and remedy are unknown. Diseased tubers will grow and produce a fair crop which may be free from disease, but the use of such seed is inadvisable. PRINCIPAL INSECT ENEMIES OF POTATO FOLIAGE. Introduction. — A few of the principal insects which feed upon potato foliage are briefly discussed here, for the reason that their ravages are often intimately associated with certain 28620— No. 2—07 2 10 View. forme of blight, and treatment for them may be profitably combined with the treatment for blight. 20 Colorado Potato Beetle, The large yellow and black -i riped beetles, commonly called " bugs," arc too common and well known to need description. This insect has migrated from the West to the East. In the Eastern State- it i- the Leading insect pot of the potato. 21 Blister Bebtli Several species of blister beetle- feed on potato foliage, frequently doing much damage, particu- larly in the Mississippi Valley. They are -lender, rather soft-bodied beetles, about one-half inch long. The two species most troublesome to potatoes are a black one and an ash-gray one. They are very active, flying readily when disturbed. They usually appear suddenly in swarms. The larvae feed on grasshopper eggs. 22 Flea-Beetles. 23 — These are small, black jumping beetle- about one-twelfth inch in length, which eat minute round holes in the leaves. Being so small and very shy they are often overlooked, even when numerous enough to do damage. They are most troublesome on sand} r soil. Frequently they do an enormous amount of damage, particularly in dry weather, when the breaking of the epidermis in so many places causes the leaves to lose water rapidly and dry up. Moreover their punctures serve as a starting point for Paris green injury and offer an easy entrance to the early blight fungus. Flea-beetles may attack the plant at any time, but in the Northern States are usually most numerous and destructive about August 1. The larvae feed on potato roots and tubers, occasionally causing a trouble known as "pimply potatoes." 24 SPRAYING TO PREVENT BLIGHT, ROT, AND INSECT RAVAGES. 25 Introduction. — Having described the principal disc: and insects affecting the potato, let us now take up the sub- ject of methods of combating them. One of the most impor- tant lines of treatment is that of spraying, which we will consider first Since about 1888 it has been known that the ravages of late blight may be prevented by spraying with Bordeaux mix- ture. 20 This has been settled beyond all doubt. More recently numerous experiments have shown that Bordeaux mixture is beneficial to potatoes in other ways. viz. it pre- 23 vents early blight, 27 greatly reduces the damage done by flea- 11 View. beetles, 28 makes it possible to more thoroughly control Colo- 24 rado beetles, 29 blister beetles, and grasshoppers, 30 prevents 25 danger of Paris-green injury, and stimulates the plants to 26 better growth and larger yield, even when diseases and insects are absent. 31 Materials, Methods, and Machinery. — Several fungi- cides have been tested and Bordeaux mixture found to be the best of all. 32 Use Bordeaux mixture made by the following formula: (1) 6 pounds copper sulphate 33 (blue vitriol) dis- solved in 25 gallons of water; (2) 4 to 6 pounds stone lime, slaked as for whitewash, then diluted with water to 20 or 25 gallons; (3) mix 1 and 2, stirring thoroughly. Use while fresh. The quality of Bordeaux depends largely upon its method of preparation. The best Bordeaux is that which settles most slowly. It is believed that Bordeaux mixtures which settle quickly are less efficient because they do not adhere so well 27 and are more difficult of uniform distribution. The best Bor- 28 deaux is made by using cold dilute solutions, uniting them 29 quickly and stirring thoroughly. 3 * (For further details of the preparation of Bordeaux mixture, see Appendix, II, page 23.) Whatever poison is used for insects may be mixed with the Bordeaux and applied at the same time. When both economy and efficiency are considered, the best two poisons for use with Bordeaux on potatoes are Paris green and arsenite of soda. The latter is considerably the cheaper, but is some trouble to prepare. (For method of preparation, see Appen- dix, III, page 25.) The quantity of poison to use with 50 gallons of Bordeaux depends on the acreage to be covered. One pound of Paris green, or its equivalent, in arsenite of soda is sufficient for an acre. Hence, if 50 gallons are applied to 1 acre, use with it 1 pound of Paris green; if applied to 2 acres, use 2 pounds of Paris green. Korse sprayers having one nozzle per row apply from 25 to 40 gallons per acre. Paris green applied with Bordeaux is more effective than when used alone, because it is more evenly distributed and adheres better. Moreover, Bordeaux itself is a deterrent to insects, being very distasteful to them. The number of applications and the time of making them will vary somewhat according to weather conditions, the prevalence of insects and disease, and thoroughness of the spraying. As a general rule, commence spraying when the plants are 6 to 8 inches high, and repeat the treatment at L2 30 31 32 33 34 intervals of ten to fourteen days as long as the plants continue green.* 1 This requires five or >ix applications during "the season. In no case Bhould the first spraying be postponed longer than the time of the first appearance of "bugs" in destructive numbers. At such time poison must be applied anyway to kill the "bugs," and it is but little extra expense to use Bordeaux with it and secure the protection it affords. For late blight the later sprayings are the most important. In fact, protection against late blight and its rot can be secured by three thorough sprayings, making the first during the blossoming period and the other two at intervals of about two weeks. From the blossoming period on, the plants should be kept constantly covered with Bordeaux mixture. Should rain come immediately after spraying before the mixture has dried the work should be done over at once. (See Appendix, V, page 26.) It is in wet weather that spraying should be most frequent and thorough, because late blight is most active then and much of the mixture is washed off by rain. The kind of sprayer to use depends chiefly upon the area to be sprayed. For gardens and fields of 1 acre or less, com- pressed-air sprayers holding 3 to 5 gallons and costing from $3 to $8 answer very well. There are also bucket pumps which may be had for the same price and which are quite isfactory. Likewise the knapsack sprayers to be carried on the back are useful for small areas, but the}' cost $10 to $15. One of these small hand sprayers is very generally useful about the garden and grounds for applying insecticides and fungicides to small trees and shrubs as well as to potatoes and other vegetables. When it is desired to use the same outfit for spraying in the potato field and in the orchard, a barrel spray-pump outfit (cost $10 to $20) is the proper thing to use. In the potato field this outfit may be used in two ways: First, it may be drawn through the field in a Light wagon or two-wheeled cart, with a man to pump and drive while two others walk and direct the spray nozzles. This method requires much man labor and is therefore expensive, but no extra outlay for apparatus is necessary and the Bpraying can be done more thoroughly than by any other method practical in large fields. Second, it may be used on a one-horse two-wheeled cart, hav- ing at the rear about '.* feet of f-inch iron, or, better still, bra-- pipe, communicating with the pump by means of a short piece of hose. To this pipe eight -pray nozzles itwo for 13 Total 55. The total cost per acre for 5 sprayings was $4. Seven rows 800 feet long were left unsprayed, but were kept free i u " . each row) are attached in pairs. One man pumps and drives, spraying four rows at each passage. All things considered, this is the most satisfactory potato-spraying outfit yet devised. It can be built at a cost of $30 to $40. For large fields of 10 or more acres geared pumps operated 35 by horsepower arc entirely practical. Several good outfits of this kind are on the market. Their chief advantage over the barrel outfit last mentioned is that the labor of pumping is shifted from the driver to the horse. They have the disadvantage in being more expensive ($60 to $100), less durable, and of heavier draft. Of spray nozzles there are many kinds. For spraying 36 potatoes Vermorel nozzles are best. They can be obtained from most manufacturers of spraying machinery. Does Spraying Pay? — Spraying rnay or may not pay according to circumstances. In some localities and in some seasons it is more profitable than in others. In the northeast- ern United States, where late blight is often destructive, the increase in }neld due to spraying is f requently enormous. At the Vermont Experiment Station the average increase in yield due to spraying during fifteen consecutive seasons (1891-1905) ** ' was 119 bushels per acre. The greatest gain was in 1893, 38 when it was 224 bushels per acre, and the least in 1900, when 39 it was 60 bushels. 30 At the New York Experiment Station 40 the average gain from five to seven sprayings during five consecutive seasons (1902-1906) was 132 bushels per acre. Perhaps farmers may not be be able to duplicate these results, but they show what is possible. In 1903 J. V. Salisbury & Sons, Phelps, N. Y., made an experiment 37 which throws much light on the subject under discussion. They sprayed 14 acres of late potatoes five times 4J with a 2-horsepower sprayer, which sprays 5 rows at each 42 passage. A record was kept of all expense of the spraying, 43 the items being as follows: 504 pounds copper sulphate, at 6 cents $30. 24 8 bushels lime, at 35 cents 2. 80 12 pounds white arsenic, at 5^ cents 66 55 hours labor for man, at 1 Ih cents 9. 63 47 hours labor for team, at 17£ cents 8. 23 Wear on sprayer 4. 20 44 14 of bugs by application of Paris green. In the fall th< row- were dug separately and weighed, aa were also 7 spn rows adjacent The yield of the unspra y ed rows was at the rate of 38 bushels per acre, and of the sprayed rows 147 bushels. Thus there was ■ gain of 64 bushels of marketable tubers per acre, worth, at time of digging, .'»' I oenta per bushel, or S*3-2. Deducting the cost of spraying, there is left a net profit of 138 per acre, or a total of $392 on the 14 m There was uo loss from rot even on the nnsprayed row-. The gain on the sprayed row- was due ohiefly to the preven- tion of late blight, thereby prolonging the life of the plants fully three weeks. Of course it is true that late blight was exceptionally severe in New York in 1903, and such results as these van not be obtained every season: but it should be noted that in this one season's work Messrs. Salisbury made enough money to spray the same acreage in potatoes during the next six years with- out loss, even if no increase in yield is obtained during that time. In other words, the crop is insured against " bugs'' and blight for six years. During four seasons (1903-1906) the New York State Experiment Station cooperated with farmers in making busi- ness experiments like the above. Forty -eight such experi- ments were made. The average increase in yield due to spraying was 52 bushels per acre and the average net profit $20.56 per acre. The same station has gathered the results of 150 volunteer experiments made by New York farmers during three seasons (1904-1906) and tinds the average gain from spraying to be 56 bushels per acre. Some argue that they do not need to spray, because in the locality in which they live late blight La rarely destructive. An experiment bearing on this phase of the subject was made by the New York Experiment Station on Long Island in 1896. 38 Eight and one-half acres of potatoes were sprayed live times with Bordeaux. Paris green being added in the first three sprayings. The sprayer used was a one-horse, two- wheeled affair operated by one man. who pumped and drove, spraying -t rows at a time. There were 4 varieties: White Elephant, Green Mountain (late). Defender (medium), and Victor Rose (early). A few rows of each variety were left unsprayed. In the fall the yield of the unsprayed rows of each variety was compared with the same number of adjacent 15 sprayed rows of the same variety. Spraying increased the yield as follows: Bushels per acre. On White Elephant 60 On Green Mountain 62 On Defender 16 On Victor Rose 5 View. 45 There was no trace of late blight on the unsprayed rows. The increased yield on the sprayed rows was due to the pre- vention of early blight, stimulation of the plants, and better control of flea-beetles and Colorado beetles. The average per- son would have said that the unsprayed rows did not suffer enough from blight and insects to materially affect the yield. Nevertheless spraying gave good results on the two late vari- eties. On the early varieties the gain was small. It is doubtful if, under such circumstances, it pays to spray early potatoes. The total expense of the five sprayings was $4 per acre. The market price of potatoes being 25 cents per bushel, the net profit in spraying the two late varieties was $11 per acre, and this in a season when there was no late blight and pota- toes were cheap. In some seasons spraying will pay well. In others there may be a loss. As the work must be commenced before it is known whether blight will appear, 39 the important thing to know is whether it pays on the average. There is little doubt that in the northeastern United States it will pay well one year with another, if properly managed; but from Ohio west this remains yet to be determined by experiment. Every potato grower who is in doubt should give spraying a thorough trial, always leaving some unsprayed rows for comparison.* We incline to the opinion that potato spra} T ing will be found profitable over all that portion of the United States lying east of the Mississippi and north of the Ohio River. The benefits of spraying to the potato crop are greatly underesti- ^" mated by farmers. A good job of spraying can be done at a total expense of $4 to $6 per acre for five applications. Philosophy of Spkaying. — Spra} T ing is preventive not curative. Once within the tissue of the leaf the blight fungus is bevond control. To be effective the spray must be applied before the fungus spores have germinated. The leaves should be coated with Bordeaux mixture, so that any spores falling 16 Vieic upon them will be unable to germinate. If the disease is thus prevented from establishing itself upon the Leaves there i- do chance for the formation of spore- to fall upon the ground and cause rot of the tubers. It is unsafe to postpone spray- ing until the appearance of the blight, for the reason that it i- usually not observed until after it has become well estab- lished and the spore- scattered broadcast Bordeaux v. Patented Fungicides. — There are upon the market numerous patented fungicides which are offered as substitutes for Bordeaux mixture. It is not profitable to use them. They are less efficient and more expensive. For pot a toes, at least, there is nothing at present known which is superior to the home-made liquid Bordeaux mixture prepared from lime and blue vitriol. Soda Bordeaux is not recom- mended; neither is dry Bordeaux mixture, except where the liquid form can not well be used. TREATMENT FOR SCAB. 47 Scab can not be prevented by spraying the tops. When soil once becomes thoroughly impregnated with the scab fun- gus it is impossible to grow potatoes fit for market, and there is nothing to be done except to plant to some other crop than potatoes for a few years. How long the scab fungus can live in the soil is not known, but it must be several years. How- ever, much of the disease may be worked out of the soil in the same way that land may be cleared of weeds, by cultiva- tion, when none are permitted to go to seed. During this process beets should not be planted on the land, for they har- bor the fungus. Neither should lime, wood ashes, or stable manure be used, for these substances make the soil alkaline and favorable to the growth of the fungus. 41 By some it is believed that the plowing under of green crops, especiallv rye, is of advantage, because it tends to make the soil acicL" Doctor Halsted. 43 of the New Jersey Station, has recom- mended flowers of sulphur applied in the open furrows at planting time at the rate of 300 pounds per acre. In some soils the sulphur treatment ma} T be beneficial, but usually it helps but little and can not be recommended. The most satisfactory method of combating scab is to care- fully guard against its introduction. As the chief mode of disl ribution is by means of diseased seed tubers, all seed should be disinfected before planting. This is best accomplished by soaking the seed tubers for two hours in a solution of formalin. 1 pint to 30 gallons of water. 44 The tubers are then spread 17 out to dry and afterwards cut and planted in the usual manner. Crates or sacks used for holding the treated tubers should, likewise, be disinfected. The disinfection may be done at any convenient time, preferably a few days before planting. The same solution may be used several times. This treatment kills the scab germs without injuring the germination of the tubers. If treated tubers are planted in a scab-free soil a clean crop may be confidently expected; but, if planted in soil already infested by the fungus, treatment avails but little. An older and probabl} T better known method of disinfection is by the use of corrosive sublimate as follows: 45 Dissolve 2 ounces of corrosive sublimate in 2 gallons of hot water in a wooden or earthen vessel; when dissolved add enough water to make 14 gallons. Soak the tubers in this solution one and one-half hours. The two methods are equally effective, but the former is to be preferred because the solution is easier to prepare, is not poisonous, and does not corrode metals. It should be borne in mind that land may become infected by the washings from scab-infested fields, by the use of manure from animals fed on uncooked, scabby potatoes or beets, and by means of implements used in cultivation. The disinfection treatment for scab will also kill any Rhi- zoctonia which may be on the tubers, but no method is known of ridding the soil of Rhizoctonia. TREATMENT FOR BACTERIAL WILT AND DRY ROT. For these two diseases no practical remedy is known. Spraying does but little if any good, because most of the trouble is below ground. On badly infested land potato cul- ture should be abandoned for several years. Tubers from diseased fields should not be used for seed. Since bacterial wilt attacks also the eggplant and tomato, these plants should not be grown on land where potatoes have been affected or vice versa. View. APPENDIX. LANTERN SLIDES. No. of view. 1. Early stage of early blight. From Vermont Sta. Bui. 72, fig. 9. 2. Advanced stage of early blight. From U. S. Dept. Agr., Farmers' Bui. 15. 3. Fungus of early blight. 1. Single spore of Alternaria solani, showing germ tubes from three cells. 2. Two spores of Alternaria solani, germinating and penetrating surface of living potato leaf; b, b, through stomates; c, through epidermis. 3. Spores of Alternaria solani, showing peculiar forms. 4. Spores of saprophytic Alternaria fasciculata occurring on potato leaves, three mature and three immature; central one germinating. 5. Fruiting branch of Alternaria fasciculata. From Vermont Sta. Bui. 72, fig. 11. 4. Tip burn. From Vermont Sta. Bui. 72, fig. 6. 5 . Late blight. Frost-like mildew on under surface of leaf. Dead brown spots surrounded on the under surface by a ring of frost-like mildew whith is composed of the spore stalks and spores of the fungus. From New York State Sta. Bui. 241, PL XL 6. Advanced stage of late blight. Lower leaves all dead and black; only few green leaves at the top. From New York State Sta. Bui. 241, PI. X. 7. Fungus of late blight. 1. Section through a diseased leaf, showing the mycelium in the tissues and two external spore stalks projecting through a stoma. 2. Spores and spore stalks more enlarged. 3. Series of drawings showing successive stages in the development of a spore. 4. Feeding threads (hyphae) running between the cells of a potato tuber. 5. Seriesof figures showing the germination of a spore: a, mature spore; d, zoospores escaping; h, zoospore beginning to germinate; i,j, k, successive stages in growth of germ tube; I, entrance of germ tube into leaf through a stoma. 6. Section of leaf showing the penetration of a germ tube into the epidermis through the cell wall. From U. S. Dept. Agr. Rpt. for 1888, PI. II. 8. Rot of tubers following late blight. Slightly affected tubers shown in cross section. From New York Cornell Sta. Bui. 113, fig. 98. 9. Bacterial wilt. Healthy and inoculated plants. Plant on left inoculated by placing on it a handful of Colorado potato beetles which had fed for some hours on diseased vines. The beetles were left on over night and gnawed the plant in many places, but did not injure it. There were no symptoms of disease until after (19) 20 IT, but after that rapid graphed three weeki after looealatli a. At thi> ti -tagesof I OH light is u heeJthj plant from the -an • as that the -; riu'l bj ::• From U. 8. Dept Agr., 1 >i\ . Veg. Phya and I'aih. Bui. 12 md 4. lO. Hill <•: potatoes partly diseased with dry rot From U. s. Dept Agr., Bureau ol Plant [ndoatry Bol 56, Erontiepii i l . Bundle blackening at stem end <>f tutors. Tub with dry-rot fangOS, Fusarium oxysporum, cut across at steal and to show the black or brown streaks. Outwardly these tubers appeared sound. Prom U. S. Dept Alt., Bureau of Plant Industry Bol 66, PL IV. i2. Tubem affected with dry end rot Late stage of the lllnrasn in stored tubers exposed to warm dry air. From U. S. Dept. Alt.. Bureau <>f Plant Industry Bui. 55, PI. VI. 13. Pongee of dry rot. Shows mycelium, spores, and germ tubes of the potato dry-rot fungus. Fusarium, oxysporum. From U. S. Dept. Agr., Bureau of Plant Industry Bui. 55, PI. VIII. 14. Tubers affected with scab. From New York Cornell Sta. Bul. 163, fig. 63. 15. Scab induced by artificial inoculation. From Connecticut State Sta. Rpt. 1890, PI. I. 16. Sugar beets affected with scab. From New York Cornell Sta. Bul. 163, cover illustration. 17. Rosette of the potato plant. 18. Rhizoctonia sclerotiaon potato tubers. From New York Cornell Sta. Bul. 186, cover illustration. 19. Hyphae of beet Rhizoctonia. Although the beet Rhizoctonia is different from the potato Rhizoctonia the feeding threads (hyphae) of the two speeies look so nearly alike as to be indistinguishable from them. Hence, we may use the beet Rhizoctonia to illustrate the potato Rhizoctonia. From New York Cornell Sta. Bul. 163, fig. 51. 20. Colorado potato beetle. From Smith's "Economic Entomology," fig. 206, and in many other pub- lications on insects. 21. Blister beetles. Three common species of blister beetles infesting potatoes: a, the ash-gray one (Macrobasu unicolor); b, the black one t Epicautu penntylraniai). From Smith's "Economic Entomology," figs. 232 and 233. 22. The flea-beetle and its work. From Vermont Sta. Bul. 72, figs. 1 and 2. 23. Flea-beetle injury reduced by spraying. Shows the number of flea-beetle punctures found in 50 leaflets from adjacent rows sprayed with different mixtOI From Vermont Sta. Bul. 72, figs. 1 and 2. 24. Damage from flea-beetlee and grasshoppere reduced by spraying. The nnsprayed rows at the right wore treated with Paris green sufficiently to prevent the Colorado potato beetle doing damage, but the flea-beetles end grasshoppers, both of which were numerous, were not cheeked. The rows at the left were sprayed three times with Bordeaux. The sprayed rows yielded 152 bushels per acre and unsprayed 118 bushels. Most of this gain was due to the action oi tht> Bordeaux as a deterrent to flea-beetles and grasshoppers. Photograph taken AJBgOSt 81, l^'.M. From Vermont Sta. Bul. 44. fig. 14. 21 No. of view. 25. Single unsprayed hill from field shown in \<>. 24. The upper leaves cut otT by gi&nhoppen. From Vermont Sta. But 44, fig. 13. 26. Single sprayed hill from field shown in No. 24. From Vermont Sta. Bui. 44, fig. 12. 27. Correct method of preparing Bordeaux mixture. The vitriol water and the limewater should both be diluted before mixing. 28. Bordeaux mixture made in different ways. Glass cylinders showing relative rapidity of settling of the precipitate in Bordeaux mixture made in different ways. Each cylinder stood one hour after making before being photo- graphed. 1. Made by pouring dilute lime into dilute sulphate slowly. 2. Made by pouring dilute sulphate into dilute lime slowly. 3. Made properly (as 5), but using hot lime milk. 4. Mixture made as in 5, but less thoroughly stirred. 5. Properly made Bordeaux mixture, i. e., from cold, dilute solutions, quickly united and thoroughly stirred. 6. Made same as 5, but using concentrated solutions. 7. Properly made mixture one day old. 8. Old Bordeaux mixture made two weeks before. 9. "Bordeaux powder" mixed with water. From Vermont Sta. Bui. 72, fig. 13. 29. Good facilities for making Bordeaux mixture. The property of W. H. Satterly, Mattituck, Long Island, X. Y., who uses it for the prepa- ration of Bordeaux for spraying potatoes. The barrel with a shovel in it contains the stock lime. The other barrel, standing against the building, contains a stock solution of copper sulphate. The two barrels in front on the upper platform are " dilution " barrels, one for lime water, the other for copper-sulphate solution. The two barrels on the lower platform are "mixing " barrels. By means of two short pieces of hose the contents of the two dilu- tion barrels are drawn off simultaneously into one of the mixing barrels. From the mixing barrel the prepared mixture runs into the spray tank through another short piece of hose. The water required comes from a tank in the barn, which is filled by means of a windmill. There is no dipping and lifting of water or Bordeaux. The work is all done by gravity. 30. Compressed-air sprayer for use in gardens. The multispray compressed-air sprayer. Capacity of tank, 5 gallons, but only about 3 gallons of liquid can be used at one time. Remainder of space is required for compressed air. Price, $5. 31. Knapsack sprayer. Knapsack sprayer. Price, $15. Capacity of tank, 5 gallons. 32. Barrel spray pumps. Two good barrel spray pumps. Price, 815 each. 33. One method of using a barrel outfit. From Vermont Sta. Bui. 72, fig. 16. 34. An excellent potato-spraying outfit. A pump in a 100-gallon tank. Sprays five rows at a time with two Vermorel nozzles per row. One man pumps and drives at the same time. Drawn by one horse. For use on hilly land a 50-gallon tank would be better. From New York State Sta. Bui. 241, PI. V. 35. A power sprayer for potatoes. Potato sprayer. Price. S75. Sprays five rows at a time with one nozzel per tow. Same sprayer shown in Xo. 41. 36. Vermorel nozzles. 37. Late blight prevented by spraying. Rows at left sprayed three times with Bordeaux. Photograph made Sept. 10. The sprayed rows yielded at the rate of 324 bushels per acre, while the unsprayed rows yielded only 100 bushels per acre, From Vermont Sta. Bui. 40, fig. 6. 38. Total yield of marketable tubers from two sprayed rows in field shown in No. 37. 29 No. of view. '.I'.K Total yield of marketable toben from two unsprayed rows in field shown in No. 4(>. Tot. it«. BfHS] tag experiment at the rk Experiment Station. Th. k- was spra\v'h» l.usl.' The unsprayed row yielded l'U hush> i- pes am-. These rows were Nor. 8, 9, and 10 in the ten year experiment ■J Genera in 1901 There was hut little rot. The increased yield on sprayed row- na- due chiefly to prolonged growth <>f the plant-. From New York State Sta. Bui. 264, PI. III. 4 1 . Bpraying in the Salisbury experiment. Another view oJ the sprayer shown in No. 35. From New York State Sta. Kill. 241, PI. VI. 4"J. Facilities for making Bordeaux in Salisbury experiment. A spring supplies the water which is piped into the larire tank at the left. 4.'$. Sprayed and unsprayed rows in Salisbury experiment Photograph taken Oct. 3, 1903. From New York State Sta. Bui. 241, PL VII. 44. Results in the Salisbury experiment. 4 5. Results of spraying when there was no late blight. 46. What spraying does. 4 7. Treatment for stab. DIRECTIONS FOR SPRAYING. I. — Copper Sulphate and Copperas. Many persons confuse copper sulphate with copperas. Copper sulphate is blue vitriol, also called blue stone. It contains copper and is used in the preparation of Bordeaux mixture. Copperas is an entirely different thing. It is iron sulphate. It does not contain copper and can not be used for making Bordeaux. The crystals of the two substances are somewhat similar in appearance, but may be readily distinguished by their color. Copper sulphate crystals are blue, while those of copperas are greenish. II. — Bordeaux Mixture. The following discussion of Bordeaux mixture is taken from Bulletin No. 243 of the New York State Experiment Station: " The essential ingredients for making Bordeaux mixture are freshly slaked lime and copper-sulphate solution. The fungicidal value lies in the copper. " The lime is added only to prevent injury to foliage and to make the mixture more adhesive and more easily seen after being applied to the foliage. Limewater will not do. A very thin white wash made from lime and water, commonly called milk of lime, is needed. The relative amounts of lime and copper sulphate which are used may be greatly varied, because a great excess of lime may be used without injury to foliage, but it is absolutely essential that enough lime be used, or injury to foliage will surely follow. It is not safe to use less than two-thirds as much lime by weight as of the undissolved copper sulphate; that is to say, in the proportion of 2 pounds of lime to 3 pounds of copper sulphate. * * * " Importance of good lime, properly slaked. — Prof. L. R. Jones and Mr. W. A. Orton, of the Vermont Experiment Station, make the following comments on the impor- tance of good lime, properly slaked: 'The quality of the lime and the method of slaking it have much influence upon the mixture. Thus, other conditions being equal, a mixture made from a poorly slaked lime settled 19 per cent (of the height of a column in a glass cylinder) in an hour, while a mixture made from properly slaked lime settled only 8 per cent in the same time. Lime that had been partially air slaked gave still poorer results. The lime should be fresh, clean, and firm. In slaking, the best results were obtained by adding at first only a small amount of water, preferably hot, and then, as slaking begins, adding cold water in small amounts as needed, never adding much at a time and never allowing the lime to become dry. When too much water is added small lumps of lime are apt to be cov- ered and remain unslaked. When the lime is fully slaked it should be fully diluted by adding water slowly while stirring.' "Strength of Bordeaux mixture. — The strength of the Bordeaux mixture may be wisely varied under different conditions. For ordinary use in apple orchards where a good spray is thoroughly applied a strength of from 1-to-ll or l-to-10 will usually be satisfactory; for treating the potato a strength of from l-to-8 or l-to-7 may well be used. For the very tender foliage of Japan plums and of peaches the mixture, if (23) 24 used at all. may be reduced to the l-to-25 formula. The designations used for the various formate are easily understood. For example, the 1-to-ll mixtore ii made by osing l pound of copper sulphate for making' 11 gallons of Bordeaux mixture. " \£ethod of pre paration of Bordeaux mixture. — It will be seen later that lime may be -laked and thus k«-pt in stock and that a stork solution of «•• »]>j>«*r sulphate may d; hut in order to gel a clear understanding of the subject the simple method of weighing ami mixing tin- ingredients will lir-t be presented. Bordeaux mixture, l t>> 10 formula. (To make .~>n gsll< H Copper -ulj .hate I blue vitriol) pound.-. . Quicklime < not slaked ) do 3J-5 Water gallon! "Stock-Inn, paste. — Several ways are known whereby the Bordeaux mixtore may be tested to find out whether enough lime has been added to unite with all of the copper sulphate, thus avoiding the necessity for weighing the lime. This permits of the slaking of considerable quantities of lime at onetime. The lime may then he kept in excellent condition for some time if covered with water to exclude the air. " /', rrocjfOtdd of potassium test — The test most commonly used for determining whether or not enough lime has been put into the Bordeaux mixture to combine with all of the copper sulphate is the ferrocyanid of potassium test, commonly called the 'ferrocyanid' test. "Potassium ferrocyanid is also called yellow prussiate of potash. It is a very poisonous yellow salt which dissolves readily in water. A few cents' worth dissolved in about ten times its bulk of water will ordinarily last through the season. In using this test fill the spray tank half to two-thirds full of the copper-sulphate solution; then pour in the milk of lime. Stir the mixture thoroughly and add a drop of the potassium ferrocyanid. If enough lime has been added, the drop will not change color when it strikes the mixture; otherwise it will immediately change to a dark reddish-brown color. More lime must then be added until the ferrocyanid does not produce the reddish-brown color. Even after the test shows no color more lime should be added, so as to be sure that all of the copper is precipitated; for in ca«e the mixture has not been thoroughly stirred some of the copper may still remain in solution in the bottom of the barrel while the test shows no color at the surface. "If the formula calls for a quantity of lime equal to the copper sulphate in weight, a half more lime than is required to satisfy the ferrocyanid test should be added to the mixture. Suppose, for example, one wished to take 6 pounds of copper sulphate and 6 pounds of lime with 60 gallons of water to make 60 gallons of Bordeaux mix- ture and to use the ferrocyanid test. When the test first shows that enough lime is present to combine with all of the copper sulphate the mixture will contain somewhat less than 4 pounds of lime. To complete the mixture according to the 6-0-60 formula requires the addition of half as much lime as has already been used; that is to say, it requires 2 pounds more of lime, or the equivalent amount of thelime paste. "Mixing tanks. — It is convenient to have special tanks for mixing the Bordeaux. Thus the tank for the lime may be placed so that its contents may be drawn off into the tank in which the copper-sulphate solution is put and in which the mixture is made. Tin-: tank may likewise be elevated so that the prepared Bordeaux mixture may be drawn off into the spray tank. By this arrangement it is possible to avoid the necessity of dipping and lifting the mixture. If these tanks are so located with relation to the water supply that the water may be run into the lime tank, it i> ble to avoid the necessity of dipping and lifting every gallon of mixture thai into the spray tank. The lime may also be Btrainedboth when it is put into thelime md when it is run from there into the Bordeaux vat, which is an advantage." 25 III. — Arsenite of Soda (Kedzie Formula). White arsenic pounds. . 2 Sal soda do 8 Water gallons. . 2 Boil until the arsenic is all dissolved, which will take about fifteen minutes. Replace the water lost in boiling, as otherwise some of the material will crystallize upon cooling. This makes a stock solution of arsenite of soda, which may be placed in tightly stoppered jugs or bottles and kept on hand for use as needed. The vessels used in making and storing the solution should be plainly labeled "Poison" and never used for any other purpose. Two quarts of this stock solution are equivalent to 1 pound of Paris green and is the quantity which should be used on an acre of potatoes. At the rate of 1 to 2 quarts in 50 gallons it may be used with Bordeaux mixture without danger of injury to the foliage, but it must not be used alone. Even with lime water it can not be safely used at a greater strength than 1 quart of stock solution with 4 pounds of lime in 50 gallons of water. IV. — Concerning the Number of Sprayings. There is great diversity of opinion as to the number of sprayings which is most profitable. Some hold that two or three sprayings are sufficient. Others would spray frequently throughout the whole season. Conditions vary so much that no invariable rule can be made. The farmer must rely chiefly on his own judgment. Probably the rule which most nearly fits all cases, and the one to be followed when in doubt, is the following: Commence spray- ing when the plants are 6 to 8 inches high and repeat the treatment regularly at intervals of ten to fourteen days as long as the plants live. Usually "bugs" must be treated when the plants are a few inches high. Often flea-beetles are prevalent at the same time. By using Bordeaux and poison together both these insects may be more effectively fought than by using poison alone. In another two weeks the second brood of bugs has appeared. A second spraying must be made for these. In two weeks more the plants are in bloom and quite large. They must now be sprayed for blight, and it is not easy to reach the lower leaves. Unless the two early sprayings have been made, it is difficult to protect the lower leaves and they fall a prey to both early and late blight. Where the vines grow large this is an important matter. Another advantage in commencing early is that the plants are always protected against an outbreak of late blight. As a rule it is unsafe to postpone spraying until the appearance of blight. Usually the blight becomes thoroughly established in a field before it is observed. In any case it is necessary to act very promptly, and there are likely to be unforeseen hindrances, such as lack of materials or the sprayer being out of order. Then, too, it often happens that the outbreak of blight occurs during a period of wet weather when it is almost impossible to get into the field to spray. The only sure way to avoid such difficulty is to commence early and spray regularly at intervals of 10 to 14 days, as above directed. One of the chief causes of failure is beginning too late. The frequency of the spraying should depend somewhat upon the thoroughness with which the work is done. In giving the above directions for spraying it is assumed that the quantity of Bordeaux applied at each spraying is at least 40 gallons per acre. If using a sprayer which applies but 25 gallons per acre, once in two weeks is not often enough. In such cases an application should be made every week. When the vines are large and the weather favorable to late blight at least 100 gallons per acre are required to do good work. The general tendency of farmers is to make too light applications. Many fail because they are too saving of time and maternal. 26 v Spb \» i v .'. Before Rain. Borne hesitate to spray potatoes when it looks like rain. They argue that the rain will trash <>ff the Bordeaux and Decessitate the work being done over. Lei us inquire into this matter. It la in rainy weather thai spraying it most needed, because it is then that the late blight spread* mosl rapidly. The beating o! the rain scatter- the Bporefl <>t" the blighl fungus ami, the conditions for their germination being excellent, infection occur- readily. Mosl of the infection takes place during rainy weather. In dry weather the disease makes slow progress because the Bporefl mii-t have mois- ture in which to germinate. Moreover, much drying kills the Bporefl outright Because of these facts the besl time to spray is shortly before rain. If there ii Bufficienl time for the Bordeaux to gel thoroughly dry on the Leaves before the rain comes, it is all right The leaves are them protected. Spores falling on them will he unable to germinate. Even when the mixture does not get dry spraying must do some good; hut in such cases another spraying should he made as soon as possible. Never Btop spraying because rain threatens. On the contrary, make a special effort to get the Bpraying done before it rains. VI. — Results of Spraying Potatoes in Vermont. Variety. White Star Do Do Do Do Polaris Do White Star Average 3 varieties. Delaware Do Do Green Mountain Delaware Do Average for 15 years. Planted. May May May Apr. May May June May May May May Mav May May May 11,1891 20. 1892 20. 1893 26. 1894 20. 1895 15. 1896 1,1897 10. 1898 18. 1899 23,1900 25. 1901 15. 1902 1,1903 25,1904 15, 1905 Sprayed. Aug. 26, Sept. 8 July 30, Aug. 13,25 Aug. 1,16,29 June 16, July 17, Aug.3( July 25, Aug. 13, 31 Aug. 7, 21 July 27, Aug. 17, 28 July 21, Aug. 10 Julv 26, Aug. 17, Sept. 8. Aug. 4, 23 Julv 20, Aug. 21 Aug. 1,20 Aug. 10 Aug. 1, Sept. 1 Aug.2,21 Yield per acre. Where sprayed. Bushel*. 313 291 338 323 389 325 151 238 229 285 170 298 361 327 382 296 Where not sprayed. Gain per acre. Bushels. 114 251 219 257 80 112 161 54 164 237 193 221 176 BusheU. 65 192 224 72 170 68 71 126 68 60 116 134 124 134 171 119 VII. — Benefits of Prolonged Growth. Few realize how great a difference in yield results from prolonging the life of potato plants two or three weeks. The following table, showing the rate of development of potato tubers at different stages of growth, is copied from Vermont Station Bulletin No. 72, page 5: Yield <>/ tuber* at different dates, White Star potatoes, planted May SO. Date of digging. Total Yield of yield per market- acre. able size. Busliels. Bushels. 58 30 115 75 230 163 304 234 356 303 379 353 Average size of tubers. August 2 A.UgUlt 12 AOgTlSt 22 September 1 . September 12 September 22 Ounces. 1.6 2 3.7 1. » 5.7 27 VIII.— Making Ex pbbi m bnib. Farmers do not experiment as much as they should. It is an easy matter to make potato-spraying experiments and not expensive. Nevertheless there are few who attempt anything along this line and most of those who do are so careless in their methods that they are unable to draw trustworthy conclusions from the results of their experiments. A fair test of potato spraying requires that an account be kept of the expense, care being taken to avoid unnecessary expense. Some rows should be left unsprayed for comparison, and these unsprayed rows should be under practically the same con- ditions as the sprayed rows. They must be of the same variety, on the same kind of soil, treated with the same kind and quantity of fertilizer, and given the same cultiva- tion. Finally, the experiment rows must be measured with a tape, not paced; and the crop on them must be weighed, not estimated. The common practice of judging the results of spraying by comparison with the unsprayed fields of neighbors is to be condemned. It is unreliable. Again, many persons, after having begun an experiment properly by leaving a few unsprayed rows, spoil it by "guessing at" the yield. Had they completed the experiment by care- fully measuring the land and measuring the potatoes on the sprayed and unsprayed rows, they would, most likely, have been astonished. A difference of 15 or 20 bushels per acre can scarcely be detected while the crop is growing, or even after the tubers have been thrown out by the potato digger; and yet this quantity is ordinarily sufficient to pay the expense of spraying. For a noteworthy example of the impos- sibility of correctly estimating differences in yield by the eye, see New York State Station Bulletin No. 241, page 263. IX. — Best Time to Dig Blighted Potatoes. When potatoes are attacked by late blight there is always danger that the tubers may rot. The question is frequently asked: "How r soon after the tops begin to blight should the tubers be dug in order to avoid, as far as possible, loss from rot?" This subject has been investigated by Professor Jones, at the Vermont Experiment Station (Seventeenth Annual Report, pp. 391-395), who sums up the results of his experiments as follows : "When potato tops have been killed by the late blight fungus and there is consequent danger of rot of the tubers, do not dig them until a week or more after the tops are killed. A longer delay will do no harm. With late varieties, where the progress of the disease is slow, do not begin digging until the third week of September at the earliest, and if practicable wait until after the tops have been killed by frost," (See Vt. Expt. Sta. Rpt. 18, p. 279, for an exception to this rule.) Our own observations lead us to a similar conclusion. If the tubers are to be stored they should not be dug until the tops are dead and thoroughly dry, in order that the fungus spores may be given a chance to dry up and die. As long as the tops remain even partially green the spores of the blight fungus continue to live. In the process of digging the tubers become covered with these live spores, and if conditions are at all favorable more or less rot results. This explains why sprayed potatoes sometimes rot more in storage than unsprayed ones. In this connection attention should be called to the objectionable practice of cover- ing piles of tubers with potato tops to protect them from the sun. If the tops have been affected with late blight they may infect the tubers and cause them to rot. The danger is especially great if the tops are green or if rain comes while the tubers are thus covered. X. — Is it Safe to Plant Where Potatoes Blighted the Previous Season? The above question is often asked. The answer depends somewhat upon the kind of blight. If the blight in question is late blight there is not much danger of the 28 being carried <»vcr in the .-oil. Bo far if known the late blight doei not live over winter in the soil. (For a diacnanon of this nbject see Conn. Kxpt. Sta. Rpt for 1906, Tart \', I-].. 903-390. i However, it seems probable that Bometimee the fangm may be carried <>\er in diseased tubers which, owing to mild weather or protection from frost, do not decay and which produce volunteer plant- the following Spring. If the blight ifl due to the dry-rot fundus ( Fuwirium o.ryxj>oruin >, or to the bai I wilt organism Bacilhutolanaoearum i, the land should not, at once, be need for pota- toes, since these diseases an- harbored from year to year in the soil. For early blight a satisfactory answer can not Ik- given. The facts are not known. XI. lii.n.in-i'Kooi Yakiki : While some varieties suffer more than others from both early and late blight, there are none entirely blight proof and probably none sufficiently resistant to make spray- ing Unnecessary. Resistance to blight is a desirable quality in a variety, but is less Important than several other qualities. Wherever late blight occur- potatoes must be sprayed anyway, and consequently the slight differences in the blight resistance of the different varieties do not amount to much. Most of the blight-proof varieties advertised are humbugs REFERENCES. 1. For a more extended and authoritative discussion of early blight see Vermont Sta. Bui. 72, pp. 16-25. 2. Vermont Sta. Buls. 49, p. 98; 72, p. 10. 3. Vermont Sta. Bui. 72, p. 12. 4. U. S. Dept. Agr., Farmers' Bui. 91, p. 10. 5. Vermont Sta. Bui. 49, p. 97. 6. For the chemistry of Paris green see U. S. Dept. Agr., Farmers' Bui. 146, p. 7; California Sta. Bui. 151, p. 3. 7. New York State Sta. Bui. 241, p. 290. 8. U. S. Dept. Agr., Report for 1888, pp. 337-339. New York Cornell Sta. Bui. 113, pp. 249-254. The statement (p. 250) that the fungus forms oospores is an error. New Hampshire Sta. Bui. 22, pp. 3-6. Connecticut Sta. Rpt. 1904, Part IV, pp. 363-384; same for 1905, Part V, pp. 304-330. 9. Vermont Sta. Bui. 49, pp. 82-83. 10. New York State Sta. Bui. 241, p. 289. 11. See annual reports of the Vermont Experiment Station, 1891 to 1906. 12. U. S. Dept. Agr., Div. of Veg. Phys. and Path. Bui. 12. 13. U. S. Dept. Agr., Bureau of Plant Industry Bui. 55. 14. For a concise resume of our knowledge of scab and its treatment see Vermont Sta. Bui. 85. 15. Massachusetts Sta. Rpt. 1888, pp. 131-138. 16. Connecticut State Sta. Rpt. 1890, pp. 81-95. 17. Indiana Sta. Bui. 39, pp. 58-60. 18. For a general account of Rhizoctonia and the diseases caused by it see New York Cornell Sta. Bui. 186, and New York State Sta. Bui. 186. A discussion of the potato Rhizoctonia is found on page 63 of the former and on page 17 of the latter. 19. Ohio Sta. Bui. 139 contains a bibliography. Ohio Sta. Bui. 145. 20. Colorado Sta. Buls. 70 and 91. 21. Minnesota Sta. Buls. 39, pp. 212, 213; 45, p. 310; Illinois Sta. Bui. 40, p. 138; New York State Sta. Bui. 101, pp. 78-82. 22. Smith, John B., " Economic Entomology," pp. 225-228. J. B. LippincottCo., Philadelphia, 1896. Price, $2.50. 23. Smith, John B., "Economic Entomology," p. 219. 24. New York State Sta. Bui. 113. 25. The best work in this country on potato blight and its treatment has been done by Prof. L. R. Jones at the Vermont Experiment Station. Potato-spraying experi- ments have been conducted every season since 1890 and the subject thoroughly inves- tigated in all its phases. The student of potato spraying should not fail to consult the annual reports of the Vermont Station from 1890 to date; also Bulletins 24, 28, 40, 44, 49, and 72. 26. Some references to the older literature of potato spraying are given in V. B. Dept. Agr., Div. of Veg. Path. Bui. 6, p. 46. 27. New York State Sta. "bul. 101, p. 74; Vermont Sta. Rpt. 18, p. 275. 28. Vermont Sta. Buls. 40, pp. 25, 26; 44, pp. 94-96. 29. New York State Sta. Bul 101, p. 75. (29) 30 30. Vennont sta. BoL 44, p. 31. Frank, B., Mid Krfiger, I . I • « den Reiz, welchen die Behandlung init Kupfer auf die Kartofielpflanae hervorbringt Her. d. deotach. boi. GeeeUech. 12, pp. B-ll; New York state Sta. BoL 941, pp. 878, 874. Vermont sta. P.ul. 72, pp. 28 Appendix, I. 84. U. >■ Dept. Agr., Farmer-* BoL 88, p. »'. An exhaustive discussion of the chemical and physical properties of Bordeanx mixture and its use aa a fungicide may be found in U. s. Dept Agr., I>iv. of Vagi Phya. and Path. Bole. *j and 9. . 35. See Appendix, IV. See Appendix, VI. 87. Reported by F. 0. BteWlH et al. in New York State Bta. Bui. 241, pp. 27 38. New York State Sta. Bui. 123, pp. 2:>>-245. Appendix, IV. 40. See Appendix, VII I. 41. Rhode Inland Sta. Buls. 26, pp. 141-155; 30, pp. 66-85; 33, pp. 51-79; 40, pp. 80-96. 42. Pennsylvania Dept. Agr. Bui. 105, pp. 84, 85. 43. New Jersey Staa Rpt. 1899, p. 345; New Jersey Stas. Bui. 112; Rhode Island Sta. Bui. 40, pp. 87-95, and Vermont Sta. Bui. 85, p. lis. 44. Indiana Sta. Bui. 65. 45. The corrosive sublimate treatment for potato scab originated with Prof. H. L. Bolley of the North Dakota Experiment Station*. See North Dakota Sta. Buls. 4, pp. 11-14; 9, pp. 27-33, and 19, pp. 131-134. 46. The Vermont Station has this subject under investigation. See Buls. 115 and 22; also. U. S. Dept. Agr., Bu. of Plant Indus. Bui. 87 and Ohio Sta. Bui. 174. O [Pot Insertion In Farmers' Institute Lecture X<>. l\] ADDENDA. Since this syllabus on Potato Diseases and Their Treatment was written the subject hap been studied more completely. It has been found necessary to vary the treatment of some of the diseases enumerated according to differ- ences in local conditions. The accompanying notes call attention to some of the points not completely covered by the syllabus, but necessary to be observed by the potato grower, depending upon his location, whether in the South, the irrigated lands of the West, or in the humid climate of the East and North. Experiments are in progress by the United States Department of Agriculture with a view to determining more accurately the efficacy of the various kinds of treatment prescribed. When these experiments have been completed the syllabus will be revised to conform to the latest information on this subject. This leaflet contains suggestions made by W. A. Orton, of the Bureau of Plant Industry, and is inserted with a view to adapting the teaching to the special conditions of the localities in which the instruction is given pending the comple- tion of the investigations now in progress. Early blight. — In the South and West the term " early blight " is often misleading, as the AUerna/ria leaf spot is more severe on the southern fall crop than on the spring crop, and in the irrigated sections it rarely becomes abun- dant until late in the fall. In either case the profitableness of spraying with Bordeaux mixture has not yet been adequately demonstrated by experiments, and can not be as confidently recommended as in the North. Late blight. — Date blight is unknown west of the Great Plains, except in limited areas on the Pacific coast. It is epidemic in the South only on the early crop, and in cool, moist seasons. Refer to B. P. I. Bull. 245. Scab.— Refer also to B. P. I. Circ. 23, and Me. Expt. Sta. Bull. 141. Dry rot. — Add to the title " and Wilt." This disease is proving one of the most widespread and serious of our potato troubles. It is particularly inju- rious in the Western States, where it is a serious obstacle to potato culture, except where a systematic rotation of crops is practiced. It is becoming increasingly prevalent in the Central and Eastern States. In many cases the disease is not conspicuous, as the vines simply appear to mature early. This early death of the foliage and the resultant* reduction in yield constitutes the greatest loss from this disease. There are also further losses from decay in storage and from failure to germinate when diseased tubers are planted. Rotation of crops and the use of healthy seed are the only means of control at present available. Two or three types of leaf -curl diseases appear to be confused at present. Some of the western difficulties often attributed to Fusarium appear to be associated with unfavorable weather and cultural con- ditions. * Rhizoctonia, Rosette, or " Little potatoes." — This disease appears in west- ern irrigated sections to be associated with heavy soils deficient in organic matter. In many localities such soils can not be profitably used for planting potatoes. The lighter types may be improved by rotations with alfalfa or other green manure crops, which are to be plowed under preceding potatoes. Rhi- zoctonia is seldom a serious trouble in the Eastern States. Internal browning. — This disease is now known to be associated with a deficiency in the available supply of soil moisture. It occurs on light or droughty soils and on varieties not adapted to the locality. The following new diseases should be mentioned : Black-leg (Bacillus phytophthorvs) . — This is characterized by the blacken- ing of the lower part of the stem when the potatoes are 6 or 8 inches high. The leaves yellow and curl upward and inward in a manner characteristic of this disease. Black-leg is commonest in eastern trucking districts. As a rule it occurs only to a slight extent, but in severe cases may destroy 25 to 75 per cent of the crop. It may occur also in epidemic form just previous to harvest 58843—12 time, causing i wn rot of the stems and tubers. It is spread on or in the seed tubers, and is controllable by the use of healthy seed. Refer to Me. Bxpt Bta. Bull. 174. Potato wart {Bynchitrimm endoMoticum) .—Th ae is prevalent in limited districts in Great Britain and on the continent of Europe, and Is charac- terised by Irregular warty OUtgrOWthS Starting near the eyes. These lire first white or, where they protrude above tin* soil, greenish In color, later becoming black as they decay. In severe cases the tubers are converted into unr< uizable warty masses, it is a dangerous disease, to be watched for and rep wherever observed, In order thai precautions rnaj be taken against It* further introductit.il and spread. Refer to B. P. I. Circ. 52 and Farmers 1 Bulletin 489. Ofkki oi Experiment Statioh Washington, D. C, July 1, 1912. I