LIB RAR.Y OF THE UNIVERSITY Of ILLINOIS 630.7 X16L NON CIRCULATING CHECK FOR UNBOUND CIRCULATING COPY i Insecticidal Control of UNDERGROUND INSECTS OF CORN A report of a 5 -year study J. H. Bigger and R. A. Blanchard Bulletin 641 UNIVERSITY OF ILLINOIS AGRICULTURAL EXPERIMENT STATION in cooperation with the ILLINOIS NATURAL HISTORY SURVEY and the U. S. DEPARTMENT OF AGRICULTURE CONTENTS Page HISTORY OF INVESTIGATIONS AND REVIEW OF LITERATURE 3 METHODS OF PROCEDURE 5 RESULTS 8 Insect Numbers 8 Insecticidal Control 12 Effects on Plant Populations 19 SUMMARY 27 LITERATURE CITED.. . .28 This bulletin was prepared by J. H. Bigger, Entomologist, Illinois Natural History Survey, and R. A. Blatichard, Ento- mology Research Division, Agricultural Research Service, U. S. Department of Agriculture. The authors gratefully acknowledge the assistance of the many farm advisers and farm operators without whose cooperation this study could not have been made. The study was supported in part by Research and Marketing Act funds allocated to North Central project 19, "Pesticide Hazards." Urbana, Illinois April, 1959 Publications in the Bulletin series report the results of investigations made or sponsored by the Experiment Station CONTROL OF UNDERGROUND INSECTS OF CORN J. H. BIGGER and R. A. BLANCHARD THE ATTACKS of underground insects on corn have been a prob- lem in Illinois from the time that corn was first grown on a large scale in this state. Entomologists have constantly sought means of controlling these pests, but it was not until the 1940's that control became practical and economical. Underground insects are especially difficult to study, because it is ? usually necessary to destroy their habitat in order to determine their presence and the extent of the damage they have done. Therefore the only feasible method of attacking these insects is the use of preventive measures. The purpose of this bulletin is to report the results of four years of investigation into control of these insects. The underground parts of corn plants are subject to the attacks of underground insects from the time the seeds are planted until the plants die or mature. Certain species attack only the seed. They are seed-corn maggot, Hylemya cilicrura (Rond.), and the two seed-corn beetles, Agonoderus lecontel Chan., and Clivina impressifons Lee. Others attack only the roots of the plants. This group includes the white grubs, Phyllophaga spp. and Cyclocephala spp., northern corn rootworm, Diabrotica longi- cornis (Say), southern corn rootworm, Diabrotica undecimpunctata howardi Barber, and corn root aphid, Anuraphis maidi-radicis (Forbes). Wireworms, Elateridae, may attack either the seeds, roots, or base of the stalk, and black cutworms, Agrotis ypsilon (Rott.) attack the stem either underground or at the soil surface. All these insects are particularly annoying pests, because their inroads on the plants are hidden until the damage has been done and it is usually not observable until too late to apply control measures. HISTORY OF INVESTIGATIONS AND REVIEW OF LITERATURE For almost a century, entomologists have constantly sought some means of preventing damage from the group of soil-inhabiting, corn- attacking insects that would not interfere with farm practices, that would be acceptable to farm operators, and that would be economical 4 BULLETIN No. 641 [April, to use. Early in the investigations it was determined that variations in cultural practices, such as rotations, time of plowing, time and intensity of cultivation, time of seeding, and similar procedures would greatly reduce damage. These measures, however, were unpopular with farm- ers because they interfered with established farm practices and often caused serious labor-load problems. In 1917, Hinds, 7 * referring to soil treatments for control of grape phylloxera in France, reported that by 1863 more than 200,000 acres of vines were being treated annually with carbon bisulfide for this pest. In 1907, Smith 9 recommended placing this insecticide into the soil around the roots of plants to control cabbage maggot, and in 1909 Newell 8 recommended it as a soil treatment to control the Argentine ant. In 1926, Davis 1 recommended using carbon bisulfide in the soil of lawns for control of white grub. During the 1907-1926 period, many other materials were tested, but none were consistently recommended. Carbon bisulfide is very expensive to use as a soil treatment, explosive when mixed with air, and dangerous to handle. Arsenic compounds were mixed in soil for white grub control very successfully, but their expensiveness precluded extensive use of them and similar materials. The possible use of repellents applied to seed was investigated in Illinois as early as 1905 and 1906. 2 At that time, 38 or more materials were used, of which the following are typical of groups: kerosene, turpentine, mustard, oil of lemon, flowers of sulfur, copper sulfate, and Scalecide. By 191 5, 3 however, recommendations stressed the use of cultural practices and farmers were warned not to use the previously tested materials in direct contact with seed. It was suggested, however, that they might be mixed with fertilizer or similar substances. Soil treatment for control of insects commonly found on the roots of corn did not become practical and economical until the introduction of chlorinated hydrocarbon insecticides and the development of machin- ery that was adequate for applying them. During the early 1940's DDT and benzene hexachloride were extensively tested. By 1946 and 1947, reports were appearing*' 6 dealing with control of the specific insects of particular interest in this study. Effective control of wire- worms and southern corn rootworms was being obtained with DDT and benzene hexachloride. Large amounts of DDT were required and its action was slow. Benzene hexachloride was used in small amounts, but imparted a flavor, especially to tubers of any sort. Reports of the use of these materials as well as lindane, aldrin, chlordane, heptachlor, parathion, and dieldrin are frequent from 1950 to the present. The earliest test in Illinois with a chlorinated hydrocarbon applied to the soil was in 1945 and 1946 (unpublished data) when DDT was * Superior figures refer to literature cited. 1959] UNDERGROUND INSECTS OF CORN 5 mixed in fertilizer in a test for control of grape colaspis. Infestation was low and results were not satisfactory. Further tests, including the use of DDT, lindane, aldrin, chlordane, heptachlor, dieldrin, endrin, and toxaphene have been carried out periodically until the present. During the earlier years, these were field tests in which one or more insecticides were applied broadcast and disked in ahead of planting, but during the later years of this period, they included granular insecti- cides and row treatments. Because of various conditions, many of these tests were failures. In some cases, infestations failed to develop in the fields. In others, the insecticides were unsatisfactory because they affected germination, or because the amount of insecticide required and the methods of application were not established. METHODS OF PROCEDURE In Illinois there are several species of underground insects of corn, no one of which is predominantly important at all times, but any one of which may be of great importance in any single year. The range of soil and climatic conditions within the state is wide. Certain insects that migrate from the South may invade the state in seasons when conditions in the South are favorable for their development. It was decided that the problem of one insect in one place could not be at- tacked, but that the entire soil-insect complex on corn would have to be studied over a wide area. Two types of tests were used a widespread pilot test beginning in 1953 and a closely controlled test beginning in 1954. Tests similar to the pilot test conducted from 1954 through 1957 will be referred to throughout the remainder of this report as the cooperative tests and the controlled tests as the experimental. Cooperative tests Cooperators were secured either by supplying a grower with insecti- cide for one or more plots, or by locating growers who were planning to treat their fields and who were willing to leave untreated areas in them. In all cooperative tests, untreated areas were left in the fields that were treated. When these cooperative tests began in 1953, 32 cooperators in the northern half of the state were furnished with aldrin emulsion for use as a spray or aldrin granules for mixing in fertilizers. Several of the cooperators applied materials to test plots in more than one field. In all, plots where insecticides had been applied were examined on 57 fields. Of these, however, there were 20 where the farm operator had 6 BULLETIN No. 641 [April, used insecticide-treated seed in the entire field. Results of this first series of tests were so encouraging it was decided to continue the pro- gram in subsequent years throughout the state. Following the experience of 1953, tentative recommendations were made for using either aldrin or heptachlor at rates of H/2 pounds of active ingredient per acre broadcast, or 1 pound in the row. These were the only insecticides used in the cooperative tests. During the last two years of the period, many farmers using insecticides mixed with fertilizers tended to apply less than the recommended amounts of insecticides. The number of tests and of fields where cooperators applied insecti- cide in the first year of a rotation is given below. Year Number of tests Number of fields 1954 103 82 1955 139 81 1956 93 64 1957 68 54 There were also a number of fields where insecticides were being applied for two successive years in a rotation. These will be considered separately. Variations in procedure on the plots in the cooperative tests con- sisted principally in amounts and methods of application and occasion- ally in delayed coverage of insecticide. Cooperators made broadcast applications of both sprays and granules. They applied sprays broad- cast as emulsions using 5 to 10 gallons of solution per acre and made row applications with sprays, or with granules using special equipment, or mixed the granules with starter fertilizer. Experimental tests From 1954 through 1957, the experimental plots were located on 17 fields on 5 farms 4 farms in Champaign county and 1 in DeKalb county. These plots were of field size, each containing an untreated area left as a check. All insecticides were put on as broadcast sprays and disked in immediately. A total of 16 tests, using single applications of insecticides, was carried out on the Champaign county farms. The insecticides used in the Champaign county tests and the amounts of actual active ingredient per acre intended to be applied were: Insecticide Ib. Insecticide Ib. Aldrin 1 ]/ 2 Chlordane 2 Heptachlor 1 }/ Endrin % Dieldrin 1 Lindane Yi Some variations from these amounts occurred. Aldrin, dieldrin, and heptachlor were used on all fields. All insecticides except chlor- 1959} UNDERGROUND INSECTS OF CORN 7 dane were used on 11 fields and all insecticides were included in 6 tests. All the tests in DeKalb county were on one farm where a 37-acre field planted to corn continuously from 1952 to 1957 was used. Plots on this field were treated in 1954, 1955, and 1956 with aldrin and hep- tachlor at the rate of li/i pounds of actual insecticide per acre. Each year after 1954, certain previously treated plots on this field were left untreated, so that eventually there were plots treated in 1954 only, in 1954 and 1955, and in 1954, 1955, and 1956. Certain areas received no insecticide throughout this period. All plots were duplicated. Un- fortunately the plots treated with aldrin in 1954 were not disked promptly and subsequent data are influenced by this fact. In addition to the Champaign and DeKalb county tests, a test was made in Iroquois county to find out how much control of Japanese beetle could be obtained with insecticides in general use for other soil insects. In this test, the amount of control obtained with insecticides sprayed or broadcast on June 1 and disked in immediately was com- pared with that obtained from a heavy application of dieldrin in granular form spread in early April with an airplane. Kinds of data From 1953 through 1957 for most fields, the kind and amount of insecticide used, method of application, whether seed treatment was also used, the crop growing on the land the previous year, plant popu- lation, and any other variable factors that might be important were determined. For 1954 through 1957, data concerning the numbers of insects present were also secured. Determinations of infestation by such insects as seed-corn maggot, seed-corn beetle, and cutworm were very difficult to make because of the short period during which their attack occurs. Relatively few records are available on control of these insects. Most records deal with control of wireworms, white grubs, cornfield ants, corn root aphids, and northern corn rootworms. Data on abundance of insects were obtained by digging up an area about a foot square that included a hill of corn or a corn plant and going down 8-10 inches to include all or much of the root system. Diggings were made at random within untreated and treated areas of each field. If the first 3 diggings in the untreated portion of a field failed to show insects present, the area was listed as uninfested and no data were recorded for abundance. At least 5 samples were taken from each plot in each infested field, and occasionally 10 or more. Damage by billbugs and cutworms was recorded as percent of plants damaged. Data were obtained on plant population (stand) by counting 25 hills or 83i/3-foot lengths in each of 6 rows in each field, 8 BULLETIN No. 641 [April, slightly less than l/25th of an acre. A statistical study indicated that 6 replicates secured as accurate data as a larger count. This type of data was considered to reflect the effect of treatment on all kinds of corn insects, including those for which digging records were inade- quate, and the difference between treated and untreated areas was considered the over-all value of treatment. Data concerning plant populations for all fields were obtained, but insect populations were recorded for infested fields only. RESULTS Insect Numbers During 1954-1957, untreated areas in 244 cornfields, or 54 to 63 fields a year, were sampled. These samples included both those from controlled experiments of field size and those from the cooperative tests. At the time of the diggings, insect infestations were important in an average of 38 percent of the fields. The range of infestation was 32 to 54 percent. Important infestations do not necessarily repre- sent a level of infestation high enough to be severely injurious, but represent an arbitrary minimum number per 5-hill sample and indicate a permanent population. Arbitrary numbers were at least: 2 colonies of cornfield ants or corn root aphids; 3 wireworms, white grubs, grape colaspis, or seed-corn beetles; 10 southern corn rootworms; and 20 northern corn rootworms. Infestations of cutworms and billbugs were considered important when 10 percent or more of the plants were damaged. During the four years, insect infestations were found to be im- portant in 92 fields (Table 1). Fifty-one fields were infested by only 1 species, 28 by 2 species, 10 by 3 species, 2 by 4 species, and 1 by 5 species. During this period, the most prevalent and widely spread injurious soil insects were wireworms, cornfield ants, corn root aphids, northern corn rootworms, and white grubs (Table 2). Other insects found were cutworms, seed-corn beetles, billbugs, southern corn root- worms, and grape colaspis. Southern corn rootworms and grape colas- pis were not very abundant during the testing period, but both have been and are potentially serious pests. Infestations of northern corn rootworms have been found in the areas north of Champaign, and southern corn rootworms largely south of there. The other insects found were distributed over the entire state, distribution depending on conditions for multiplication. To forecast damage has been impossible, but observations in this study indicate that fields in corn 2, 3, or more years, or in corn follow- ing clover-grass or alfalfa-grass mixtures are most likely to be in- J959] UNDERGROUND INSECTS OF CORN G CROP ON SOIL INSECT POPULATIONS: Number and Fields Infested; 244 Fields; 1954-1957 u O u C 4> > C 9* 89 o ^- u O u:S8 6 111 2 a CL. . . 4> * . o cn <- C S a> **! -C 5r^ H g B S ^1 "J o QJ * r^ C fe 4J g Q rv. c *^ ti CC OJ J-H J2 W O rti ^ i^- 1 X '-ti 1 r" C Tl T"! C **"* flj flj i- 1 +j T3 c co V . . . . C ,J2 *2 *C ' ; ; * ^_ C^H ^ " H a i - * -2 c c O O '"^ : : : : ^ 2 g " u c c : 1 '"* 5eN ~ H ll^^ 10 BULLETIN No. 641 [April, IM JB ^OOO-^OO-^OOO <*5 6 - a 2 u g 00 .0 1 v t^ -^ T-H ^-H ^-H *-t VO M-H I **! ! ^ 4 y n? \ W ' ~1 QJ TH -* .^j TO vOvOOv^OfJisjO-^rOfT!'-' 1* f y^ o ^ ^ g 2 2 ^ * ^ ^ ^ t r O 1 C h J rt ^ H - X ~' b * ) qj 'S. L> cn^^SxiS- 8cS c- a _. c 2^S c p c"o"^ O Ti Ti ^ bfi ^ o u< vri *~* ^ ^ H illllllJllF 1959] UNDERGROUND INSECTS OF CORN 11 fested with the insects found in the digging operations (Table 2). Fields planted to corn after small grain, soybeans, or bluegrass are least likely to be seriously infested. Infestations in second-year corn sometimes carry over from previous crops. In at least one instance, white grubs, which have a 3-year life cycle, infested both first- and second-year corn following a straight corn-soybean rotation. In other instances, billbugs seriously damaged corn in fields planted to corn the second year as well as that planted to corn for 3 years or more. These infestations were only coincidental, however, since the billbug infestation apparently depended on nutgrass in low areas in fields and in ditches around the borders of the field. Billbugs are most often found in bottomland fields in river valleys and in old lake bottoms. The rotation is only secondary since the larvae feed on wild swamp-type plants, and the adults cause the damage by boring into the young seedlings. According to Illinois Natural History Survey records, populations of northern corn rootworms became large enough to cause severe lodging only where corn had been grown on the same field for 3 years or more. No large reductions in yield occurred following rootworm attack. Rootworms, however, cut off the roots of the plants and cause them to lodge. Lodging makes harvesting difficult and causes con- siderable actual harvest loss. Counts in several fields infested with rootworms showed picker loss on untreated plots to be double that on treated plots. Cutworms have caused serious damage in fields in corn a second year, in fields in cotton the previous year, and in corn following alfalfa-grass mixtures, or bluegrass sod. Wireworms tend to occur most often in damaging numbers in corn following a legume-grass crop, or in second-year corn. While they were frequently found in second- year corn, they were often carried over from the legumes or other plowed-up crops, since most species have a life cycle of 3 years or more. While they were found in fields in corn 3 years or more, they caused less serious damage in such fields. Cornfield ants were found in corn following almost every crop, but colonies of corn root aphids were found associated with them most often in fields in corn 2 years or more and less often in corn following small grain or bluegrass. They were never found in corn following a legume-grass or soybean crop. Serious damage from cornfield ants and corn root aphids occurred very rarely although they were among the most numerous of the soil insects found. At one time 2 corn root aphids were rated as one of the most injurious insects on corn in Illi- nois. Adoption of rotations, the use of hybrid corn, increase in 12 BULLETIN No. 641 [April, general fertility of the soil, or a combination of these and other factors has lessened the damage they do. Since seed-corn beetles and seed-corn maggots damage the sprout- ing seed and since it was not possible to examine many fields during the early seedling stage, it was not possible to get good records on the damage they do. Losses from these insects are reflected in the counts of plant populations that will be discussed later. Predictions of the abundance of soil insects is, for the most part, very uncertain, as should be apparent from this discussion. In many cases, farmers will have to depend on the history of particular fields on their farms, or carry out preventive control measures as a kind of crop insurance. Insecticide I Control Experimental tests Soil insect infestations were not significant on several of the experi- mental plots, but infestations did provide some information on control of 9 insects. In a number of cases, an insect was present in only one of the tests. In these cases, apparent differences in control between insecticides are probably not significant. All tests showed that aldrin and heptachlor at 1.1/2 pounds an acre and dieldrin at 1 pound an acre gave good control of all the insects that occurred in these plots (Table 3). Chlordane at 2 pounds an acre gave good control of wire- worms, but was not as good for control of cornfield ants. The other insects did not occur in plots where chlordane was applied. Endrin and lindane at 1/2 pound an acre did not give good control of certain insects. At present prices, these two insecticides could not profitably be applied at much higher rates, so were not tested further. Aldrin and heptachlor at li/2 pounds an acre, chlordane at 2 pounds, and dieldrin at 1 pound an acre controlled wireworms and white grubs for at least 2 years (Table 3). Data (not included in this report) indicated that 2 years after the insecticides were applied aldrin gave no apparent control of seed-corn maggot, while heptachlor gave 33-percent apparent control. Lindane at 1/2 pound an acre gave perfect carry-over control of wireworms and corn root aphids a second year, but poor control of white grubs. Endrin at 1/2 pound an acre gave perfect control of white grubs a second year, but poor control of wireworms, cornfield ants, corn root aphids, and grape colaspis. In a single test, aldrin and heptachlor at li/ pounds an acre provided excellent control of grape colaspis. Lindane at the same rate proved somewhat less effective but gave good control. In one experimental test where the insecticides were sprayed broad- cast and disked in immediately before the corn was planted, aldrin, UNDERGROUND INSECTS OF CORN 13 tf^.O--^ Oroi-0^ c KOv -O O O^OOOOO CO ^Xj o _c 1 c "^j ^5 **^ ' ON C^ ^5 $"* ^^ ^^ *c T3 |^ :* : : ; C W _, ^ 04 .^ . .^ . . O . . 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All the insecticides appeared to give good to excellent control of northern corn rootworms. In one experiment on the DeKalb field, heptachlor appeared to kill a minimum of 92 percent of northern corn rootworms for at least 4 years (Table 3). For the same period, aldrin gave a minimum of 63-percent mortality. It was somewhat less thoroughly applied than heptachlor, and under the same conditions might have been equally effective in control of northern corn rootworm. The test on Japanese beetle control (Table 4) showed that 2 pounds of dieldrin to the acre in granular form applied by airplane in April before the soil was plowed killed 100 percent of the full grown over- wintering larvae. Aldrin and heptachlor at ll/ pounds to the acre sprayed broadcast and disked in the first of June did not effectively control the full-grown larvae. Both insecticides, however, gave ex- cellent control of newly hatched larvae. It appears that general rec- ommendations for control of soil insects will control Japanese beetle as well as other white grubs. Observations also indicated that cultural practices, as well as natural factors, greatly reduced the Japanese beetle populations in corn and soybean fields. Cooperative tests Much better information concerning control of soil insects with two insecticides, aldrin and heptachlor, was obtained from farmers' fields than from the experimental plots, largely because there were more observations in farmers' fields and the chances for suitable insect infestations were greater. Also farmers used a number of different methods of application and a number of different rates. These var- iables gave some data on the effects of those factors on control. (For information concerning control of eight insects or groups of insects with aldrin and heptachlor at recommended or less-than-recommended rates, see Table 5.) Minimum recommended rates, based on data obtained in 1953, were l^i pounds per acre of active ingredient applied broadcast, or 1 pound per acre applied in the row. It was recognized that variations were bound to occur. Therefore, under recommended dosages in Table 5 were included instances in which farmers applied at least 1.3 pounds of the insecticides broadcast or 0.8 pound in the row. (For data on the several methods of applica- tion farmers used, see Table 6.) Only recommended dosages were included in Table 6. The results and recommendations and certain authentic observations by farmers given in the following paragraphs are taken from these tables, 5 and 6. 1959] UNDERGROUND INSECTS OF CORN IS gc -0-0 .2 -3 "o !_, "~"3 Q^ 03 S U 10 O O O\ 10 00 O O O ^t 4 O OO O 4) 0.1- fe ^H . ^^ JQ E O O S 4) fjj u <42 _Q H M o C 03 TJ & 4) 4) _s ^ rt rt rO rO ^ ^* l/"5 t^ 10 *^ O U ' 00 OO CN - CN rt C/) -S 03 T-H ^ 1 . . h c g ^ T3 o a 4) 't- C ^ ^ " ^ ^ T3 "rj C*j3 53 10 *O O ID ro O O o Bit* * O\ ON O 'i CN O ^ "o O< O o '^ 41 < E a 3 ^ TJ m C " 4) _. 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O O 1_ U, U m Ui ^ U* ^ |1 OTJ^JJ o bCo3-" ^ J^ Si 3) hchCcS (U 2 4) C "S. 52 a - eg a; tg qj T* *^ "r" S SO bo g c c 'C b^o ' >9 M v -nOj-itJ^O^O^O <, W W i i ^"C'CTJ 1 rt 4^ rt -^ rt .3 o; B rf c M cd Q^ rt p> l rt Q^ s .fl o *c c g ^-7345 a ~z "q l !^ a a a O^^--2 41 .5 2 zcucuQ +J CN T^ ^-H O t*~ ro O ^H ^ i ^-i Q ^fl r^ ^-H 1 o^ T-l Z 1 I wT c G o r-H C O v i: o! *^ O ;r" ^, t> *-* to _o u C 4> O 00 r- O O ON 00 t^- O ^tj O i "2 2 en 4> bfl CJ rt "5. OH "E a rt O C 'C o 2 ' 2 1 OO^t < '4> rt *S i W c rt "^^ ti ; c i C/3 < w 3UIUIO33 c Percent control ^^ o {^ gOOO\O\O\Ot^t-~O S, 'OOO - -as .S 2 1 < K 2 "^ 2 w <2 tn a) ^2 g c 5 *g i o ^ tn O o 3 S S * J " (M ^^ CN " O rt u ! -. Z u rt ^ u o E I f T l C 3 ** 3 Q i>* !-. S c g H V 7 I *^ S ? ^o 1 t^ o : rt rt J3 tr* &, " H H ^~ ^<3 rt > "2 T3 U H O ^- OJ > ^. C 'S H X rt S.S u > ,~ 03 4; H '' o-!C -" "2 o (/a ^ o c ' PH rt ." - 5 tn f S C / 0) in in tr en rn u a c^ H C E E : E E ^ > S.S O o ^ O 2 -S T3 H 5 4-1 .2 Hj Sj * _O o S / ) 80 o o O tn en o o ^ ^ u"?."3. "^ u. rt c c _2 IS "gj ^ t " c ^2* j:: ^ v x^'S* > ""-^ Sort" 3 -^ ^Syrt" 3 - "a'gl > 3 a il|li|li fill ill !.% & ? f 4 IllllJui illljol 1959} UNDERGROUND INSECTS OF CORN 17 Lg c"o 3 4_> u i 8ir> .... II _ c N '^ ^ OJ O c"o II OJ o DH ^ OOv -O 10 oo ^ 1 t^ 1 1-1 [ >. c i t,-, t 13^ | -s __ OOSCNOOO R C Z Js +J 1 *""* 1 C j .2 i j c"o 1 1 i i tO "5. a ed "o a o (U O 2 ^ n 4-1 i i 0) ! **" fcrj ^ S c"o ' wT ) ~ _c OJ li O) O P-, O CN ^O iO \O ON *-i iO 3 ^ i ^ u ' "o tn i "> > H O u In S. 5 a) C4rooor4^00 H O t^iO o *T3 en vi c oo OO ON CO f"~ OO OO t^* >, u 0) o Cu o ^ ) 2"rt \ $2 S^ -2 ) h3 OJ 4> CN -( 4 * *" H 1 1 H > \ ^ * . tn t/5 J 4- . :g g H tL O o 9 .>.... 5 C 4J 4^ : 2 :^J * ' C C r/i *r^ "trj 3 ^ U-i i_ *-* Q, ^j J ^ JD 8 8 c3 rt ^ c2cc"co c c Q tuO *" t^ *T^ O O U< H D .-^ -M +j C C -0 !^ *" ~~ O ^ O O ^ "S I -a T3 C J 'O & rt ^ P -S u 3 3 i "5 7^ C. 18 BULLETIN No. 641 [April, Wireworms. In general, aldrin and heptachlor were about equally effective although in 1957 some near failures occurred with aldrin. Dosages of 1J/2 pounds per acre sprayed broadcast and disked in, or 1 pound in liquid sprayed in bands over the row gave the best control. Insecticides in granules or in dry fertilizer applied at planting time or in dry fertilizer applied in the late fall or early spring were less effective. Large, full-grown wireworms 2 or 3 years old were very difficult to kill. Dosages well above those recommended for general use dosages up to 3 pounds per acre would be required to control them. Fortunately, wireworm infestations seldom comprise only full grown larvae. White grubs. Aldrin in general gave somewhat better control than heptachlor. Applications of 1 1/2 pounds to the acre broadcast or 1 pound in the row are satisfactory except where large 2- and 3-year old grubs occur. Then 3 pounds to the acre are necessary. This is especially true where corn is grown in a corn-soybean rotation. The rotation allows the May beetle, Phyllophaga rugosa, to lay its eggs in the soybeans and to become very abundant at times. Experience has shown that where the grower is dealing with a heavy infestation of these large grubs, the insecticides should be applied at least 2 weeks before the corn is planted. Otherwise the big grubs can destroy large numbers of the young corn plants before the insecticides become fully effective. The method used to apply the insecticides had no apparent effect on control. Northern and southern rootworms. Aldrin and heptachlor at 1 pound per acre broadcast as sprays or broadcast in fertilizers were equally effective. Applying insecticides in the rows was not tested. These insects appear to be easy to control with insecticides. Even smaller dosages than those recommended gave good control for at least 2 years as long as observations in these particular fields ran. As was shown earlier Table 3 experimental tests gave good ap- parent control of northern corn rootworm for as long as 4 years when heptachlor was applied as a broadcast spray at the rate of \l/2 pounds to the acre. Cornfield ants and corn root aphids. These insects were controlled when li/2 pounds of aldrin or heptachlor were applied as broadcast sprays. The insecticides were not effective when applied in the rows. It appears that the ants were able to detect the insecticide and when it was placed in the rows, avoid it, but, of course, they could not avoid it when it was broadcast. Numbers of ant colonies with accompanying aphids were found between the rows in fields where row applications of insecticides were made. In one year, after 1 pound of aldrin was 1959] UNDERGROUND INSECTS OF CORN 19 sprayed broadcast, ant and aphid colonies were apparently reduced only 44 and 47 percent respectively. No records of carry-over control with heptachlor or aldrin at dosages of over 1 pound per acre were obtained. Cutworms. Aldrin and heptachlor at 1 1/2 pounds per acre sprayed broadcast and disked in gave fair to good control in the cooperative tests and in one experimental plot. Farmers' reliable observations have shown that 1 pound of aldrin sprayed in a band over the row at plant- ing time gave excellent control. Fields treated in 1956 with lJ/2 pounds of aldrin per acre -were observed to be severely damaged by cutworms in 1957, indicating little or no carry-over control from one year to the next. Corn billbugs. Both aldrin and heptachlor have been used to con- trol corn billbugs, which often cause losses in bottomland or in other areas where nutgrass grows in or around the fields. The minimum dosage necessary for good control was not determined, but dosages of aldrin or heptachlor at 2 pounds per acre have given good control in some other areas. Tests in Illinois and elsewhere indicate that the billbugs migrating into a cornfield from the outside are not killed the year following treatment. When ditches, field borders, or grass water- ways in or near a field to be planted to corn have heavy growths of nutgrass, they should be treated with aldrin or heptachlor if the field has a history of billbug damage. Effects on other soil insects. Both aldrin and heptachlor destroyed most of the ground beetle larvae, which are predators of soil insects. However, none of the insecticides tested in either farmers' fields or experimental plots adversely affected the earthworm populations. In fact, the earthworm populations in areas treated with insecticides appeared to be somewhat larger than those in untreated areas. Effects on Plant Populations Experimental tests Counts of plant populations were made on all experiment fields to determine the over-all effect of the soil treatments. Results on the fields in Champaign county showed there were more plants on the treated than on the untreated areas (Table 7). Data show that differ- ences in favor of treatment were significant at the 1 -percent level for aldrin, dieldrin, and heptachlor, the insecticides included in all 16 tests. In 11 tests, including all insecticides except chlordane, differ- ences in favor of treatment were significant at the 1 -percent level for aldrin and heptachlor, and at the 5-percent level for dieldrin and endrin. In 6 tests where all insecticides were used, differences in favor 20 BULLETIN No. 641 [April, Table 7. EFFECT OF TREATMENT ON PLANT POPULATIONS: 16 Tests; Experiment Fields; Champaign County, 1954-1957 Increases resulting i :rom treatment Insecticide and number of tests Number of plants per acre Percent Sixteen tests Aldrin 786** 6.7 Dieldrin 521** 4.2 Heptachlor 642** 5.2 Eleven tests Aldrin 891** 7.3 Dieldrin 686* 5.6 Heptachlor 739** 6.0 Endrin 445* 3.6 Lindane 403 3.3 Six tests Aldrin 671** 5.2 Dieldrin 571** 4.4 Heptachlor . . 461* 3.6 Chlordane 113 0.9 Endrin 396 3.1 Lindane. . . 296 2.3 Note: two asterisks indicates a significant difference at the 1-percent level; one asterisk indicates a significant difference at the 5-percent level. of treatment were significant at the 1-percent level for aldrin and diel- drin and the 5-percent level for heptachlor. Plant populations on plots treated with either lindane or chlordane were not significantly higher than populations on the untreated plots of the field. On the experimental field at DeKalb when aldrin was used, plant counts indicated a declining residual effect 1 and 2 years after a single treatment (Table 8). This was not true on the plots treated with hep- Table 8. EFFECT OF TREATMENT WITH ALDRIN AND HEPTACHLOR ON PLANT POPULATIONS: Experiment Field, DeKalb; 1954-1956 Increases resulting from treatment Year data recorded Years treated Aldrin Heptachlor Number of plants per acre Percent Number of plants per acre Percent 1954.. 1954 1954 1954-1955 1954 1954-1955 1954-1955- 1956 1,258 734 2,646 524 1,572 393 8.4 5.6 20.1 3.7 11.0 2.8 524 472 917 917 917 891 3.5 3.6 7.0 6.4 6.4 6.3 1955 1955 1956 1956... . 1956 1959] UNDERGROUND INSECTS OF CORN 21 tachlor and may indicate heptachlor has a longer residual life. Hepta- chlor tends to remain in its original form over a longer period than aldrin. 4 The relatively small differences in 1956 in the aldrin plots treated 3 successive years may possibly be due to planter trouble. Otherwise, they are inexplicable. Cooperative tests During 1953-1957, cooperators made 352 tests with aldrin or hepta- chlor applied on fields being treated for the first time in a rotation. These tests were on fields in which the seed in neither the treated nor untreated portions of the field had been treated with an insecticide. These treatments included applications broadcast as sprays or granules and disked in, and row treatments either as sprays or granules applied with special attachments on the planter or applied as insecticide- fertilizer mixtures. They also included varying amounts of insecticide, depending on the accuracy with which the farmer calibrated his equip- ment. Over 310,000 plants were counted on these plots. The treated areas contained an average of 9,643 more plants than the untreated areas (Table 9). This is an average of 718 or 6.3 percent more plants per acre per field. In 1954 and 1955, careful counting and weighing of representative areas showed that an increase of 350 plants per acre on the treated areas paid for the insecticide and application. Sixty-seven percent of all treated fields showed that much increase. Comparison of insecticides, Cooperators' fields No heptachlor was used in 1953. In each succeeding year, however, both heptachlor and aldrin were used and results with each compared Table 9. EFFECT OF TREATMENT WITH ALDRIN AND HEPTACHLOR ON PLANT POPULATIONS: All Treated and Untreated Areas; First Year of Treatment; 352 Cooperators' Fields; 1953-1957 Year Number of tests Total number of plants Increases resulting from treatment Treated areas Untreated areas Number of plants Plants per acre Per- cent 1953.. 37 16,361 44,663 43,503 29,795 28,728 163,050 14,916 41,655 41,429 27,904 27,503 153,407 1,445 3,008 2,074 1,891 1,225 9,643 1,024 765 584 773 582 718" 9.7 7.2 5.0 6.8 4.4 6.3 1954 . . . 103 1955 93 1956 64 1957 55 1953-1957 . . . 352 a Differences resulting from treatment were significant at the 1-percent level. 22 BULLETIN No. 641 [April, Table 10. EFFECT OF ALDRIN AND HEPTACHLOR ON PLANT POPULATIONS: 34 Tests; Cooperators' Fields; First Year of Treatment; 1954-1957 Increases resulting from treatment Num- Total number of plants Aldrin treated areas Heptachlor treated areas Year ber of tests Un- treated areas Aldrin treated areas Hepta- chlor treated Num- ber of Per- cent Num- ber of Per- cent areas plants in- plants in- per crease per crease acre acre 1954.. 2 710 772 742 810 8 7 419 4 5 1955 8 3,813 4,203 3,978 1,279 10 2 542 4 3 1956 14 5,972 6,575 6,501 1,127 10 1 990 8 9 1957 10 4,624 4,786 4,971 424 3 5 909 7 5 1954-1957 34 15,119 16,336 16,192 938" 8.1 825 a 7.1 a Difference between aldrin and heptachlor not significant. Each treatment was signifi- cantly better than untreated areas at the 1-percent level. to a common untreated area. During the 4-year period, 34 such tests were conducted involving counts of over 45,000 plants. The plots treated with aldrin contained an average of 938 or 8.1 percent more plants than the untreated plots (Table 10). The plots treated with heptachlor contained an average of 825 or 7.1 percent more plants than the untreated plots. Statistical analysis showed no significant difference between treatment with aldrin and heptachlor, but as against the untreated plots, each was significantly better. Neither was con- sistently superior to the other, the order of apparent effectiveness changing from field to field. Broadcast treatment compared with row treatment, Cooperators' fields During 1954-1957, a total of 239 tests was checked. These were tests in which some factor other than method of application did not confuse the results. They included 180 tests in which insecticides as sprays or granules were broadcast and 59 in which they were applied in the row. They included insecticide-fertilizer mixtures. They exclude fields on which less than recommended amounts of insecticides were used. About 218,000 plants were counted in these fields. The broadcast treated areas contained 789 or 6.8 percent and the row-treated areas 542 or 4.6 percent more plants than the untreated areas (Table 11). Thus broadcast treatment gave significantly better results than row treatment, but the results with row treatment when recommended amounts of insecticide were used were still profitable. The best results 1959] UNDERGROUND INSECTS OF CORN 23 Table 11. EFFECTIVENESS OF BROADCAST APPLICATIONS COMPARED WITH ROW APPLICATIONS: Recommended Amounts of Insecticide; First Year of Treatment; 239 Tests; Cooperators' Fields; 1954-1957 Number Total number of plants Increases resulting from treatment Year of tests Untreated areas Treated areas Plants per acre Percent increase 1954.. 56 Broadcast-treated areas 21,749 23,457 18,119 19,158 16,099 17,681 23,527 24,608 79,494 84,904 Row-treated areas 7,942 8,351 9,665 10,151 5,428 5,600 3,277 3,435 26,312 27,537 799 697 1,090 613 789" 595 579 377 592 542" 7.9 5.7 9.8 4.7 6.8 5.1 5.0 3.2 4.8 4.6 1955 ... ' 39 1956 38 1957 47 1954-1957 . . 180 1954.. 18 1955 22 1956 12 1957 7 1954-1957 59 * Difference between methods significant at 1 -percent level. with row treatments were obtained when insecticides were placed over the row. (Note: this test was also conducted in 1953, but data for it were not included in Table 11 because many of the results of row treatment were confused by the use of seed treatment also.) Amounts of insecticide used Following the 1953 season, the use of li/^ pounds of active in- gredient per acre was recommended for use broadcast and 1 pound for use in the row. The results with recommended and less than recom- mended amounts of insecticides were compared. The tests included broadcast and row treatments and sprays or granules of both insecti- cides. In the 288 tests in which the results of using recommended and less than recommended amounts could be studied, 236 were made with recommended and 52 with less than recommended amounts of insecti- cides (Table 12). In the tests using recommended amounts, there was an average of 736 or 6.3 percent more plants per acre on the treated areas than on the untreated. When less than the recommended amounts were used, there was an average of 519 or 4.6 percent more plants per acre on the treated than on the untreated areas. The difference is significant at the 1-percent level. Many of the unsatisfactory results obtained with row treatments in 1956 and 1957 were in fields on which insecticide-fertilizer mixtures were used. During 1954 and 1955, in several of the fields on which 24 BULLETIN No. 641 [April, Table 12. EFFECTIVENESS OF TREATMENT WITH RECOM- MENDED COMPARED WITH LESS THAN RECOMMENDED AMOUNTS OF INSECTICIDE: 288 Tests; 1954-1957 Year Treated with at least recom- mended amounts 8 Treated with less than recom- mended amounts Number of tests Increases resulting Number of tests Increases resulting Plants per acre Percent Plants per acre Percent 1954 76 747 652 935 624 736 h 6.9 5.5 8.3 4.8 6.3 21 14 14 3 52 752 511 257 157 519 b 7.4 4.6 2.2 1.1 4.6 1955 59 1956 50 1957. 51 1954-1957 236 a Considered recommended amount if 1.3 pounds or more was applied broadcast or 0.8 pound or more was applied in the row. b The difference between these two figures is significant at the 1-percent level. less than recommended amounts of insecticide were used, rootworm, which is easier to control than some insects, was the only insect prob- lem. Practically all the data for these two years came from fields where insecticides were applied broadcast. Effect of position in the rotation During 1954-1957, information from cooperators allowed the study of the possible effect of previous crops on the effectiveness of soil treatments on 289 fields. These fields included all methods of applica- tion and all amounts of insecticides. The figures indicated that for the 4 years treatments were economical in all cases (Table 13). The economy effected, however, varied from year to year and field to field, depending on the prevalence of one or more insects in any field in any one year and can be expected to vary in the future. The greatest advantage of treatment appeared to be in second-year corn and the least following alfalfa or an alfalfa-grass mixture. The 4-year aver- ages, however, were not significantly different. On the basis of this information, no prediction can be made concerning the fields on which treatment is likely to be most profitable. Effect of treatment in two successive years During these studies, there was opportunity to examine 26 fields where soil treatment was applied for the second year in succession. All were fields where recommended amounts of insecticide were broad- cast. They were on land where the entire field had been treated the first year and a portion of this area left untreated the second year. UNDERGROUND INSECTS OF CORN 25 M-H O u en . S s S rH CM O """ *- \o , M C o C u Jj 3 i' 26 BULLETIN No. 641 [April, The figures for this test are given below. Increases resulting from treat- ment for 2 years in succession of Number of Year tests plants per acre Percent 1954 2 1,205 13.4 1955 4 262 2.3 1956 16 432 3.5 1957 4 935 9.6 1954-1957 26 545 a 5.1 a Difference significant at the 1 -percent level. These data show that there was an average of 545, or 5.1 percent, more plants on the areas treated the second successive year than on the area treated only the first year. This difference is significant at the 1 -percent level. Although these data do not appear to conform to insect control records for the year following treatment, they show control of insects not included in the insect control records (Table 3) and may be largely a result of control of cutworms, seed-corn mag- gots, and seed-corn beetles. Seed treatment tests During the course of the testing program, there was opportunity to test seed treatment applied by the farmer as compared to soil treat- ment. In most cases in 1953 and 1954 the insecticide was lindane and the following years dieldrin. In all cases recorded (Table 14), the insecticide was applied to the seed in the planter box at the rate rec- ommended by the manufacturer. In 43 tests, all the seed used in a field was treated and a portion of the field also received soil treatment. These tests showed an average of 742, or 7 percent, more plants per acre when soil treatment was superimposed on seed treatment than when it was not. In other cases, a portion of the field was planted with treated seed, a portion was given soil treatment, and a portion was given no treat- ment. In 15 such tests, the area planted with treated seed contained 765 fewer plants per acre than the untreated area, a decrease of 6 percent. But the portion of the field given soil treatment contained an average of 857 more plants per acre than the untreated area, an in- crease of 6.8 percent. Effect of treatment on yield During the period of the tests, yield data were secured on 55 plots where hand-picked samples were taken. Increased yields for treatment ranged from to 21.4 percent and averaged 6.8 percent. The greatest 7959] UNDERGROUND INSECTS OF CORN 27 Table 14. EFFECT OF SEED TREATMENT ADDED TO PLANTER BOXES AND SOIL TREATMENT WITH AND WITHOUT SEED TREATMENT: 58 Tests; 1953-1957 1953 1954 1955 1956 ' 1953 ~ 1 ( >57" 1957 Soil treatment superimposed on seed treatment Number of tests 20 7 16 43 Increased number of plants on soil-treated over seed-treated areas Number of plants* per acre 922 736 514 742 Percent 9.6 6.9 4.4 7.0 Seed treatment compared with soil treatment, same fields Number of tests 7 6 2 15 Difference between number of plants on treated and untreated areas Seed treated Number of plants per acre -1 454 162 1 140 -765 Percent -11 2 13 -97 -6 Soil treated Number of plants per acre 867 1 009 354 857 Percent 67 8 3 6 8 Combined because of small number. increases occurred in fields known to have relatively severe infestations of wireworms, grubs, and cutworms. Some failures to show increased yields from treatment occurred where drouth had reduced soil moisture to such an extent that the larger plant populations in treated areas actually caused the entire plant population to suffer. The insecticides used and the rate of use in these tests did not affect the corn plant directly, but indirectly affected it by controlling the insects feeding on it. SUMMARY Cornfields in Illinois, as this 5-year study shows, may be damaged by one or more of these underground insects: wireworms, white grubs, grape colaspis, cornfield ants, corn root aphids, or rootworms. They were present in significant numbers in 38 percent of the fields studied and may do considerable economic damage. The extent of infestation was determined by digging in untreated portions of cornfields throughout the state. Abundance of the insects mentioned above appears to be most likely when corn is grown more than two years in succession in a field or when corn follows a legume-grass mixture. 28 BULLETIN No. 641 Cornfields are also damaged by seed-corn maggots, seed-corn beetles, cutworms, billbugs, and possibly other insects. Plant population counts suggest that such damage may occur in an added 30 percent of the fields. Over-all damage by these insects was measured by counts of plant populations in treated and untreated parts of the fields. Aldrin and heptachlor at a rate of 11/2 pounds of active ingredient to the acre and dieldrin at 1 pound to the acre, all sprayed broadcast and disked in ahead of planting, gave good to excellent control of all insects under study. They also provided the largest increases in plant populations in the treated portions of the fields. Aldrin and heptachlor at 1 pound per acre, broadcast and disked in, gave very good control of corn rootworms. These insecticides at 1 pound per acre applied over the row and covered with soil controlled most, but not all, the insects studied. Insecticide-fertilizer mixtures used at planting time and placed in the row were not always effective, especially if less than 1 pound of insecticide per acre was used. Insecticides at rates recommended are not detrimental to the plants. They destroy some predators but do not reduce the earthworm population. LITERATURE CITED 1. DAVIS, J. J. Common white grubs. U. S. Dept. Agr., Farmers Bui. 940. 1926. 2. FORBES, S. A. Experiments with repellents against the corn root aphis, 1905 and 1906. 111. Agr. Exp. Sta. Bui. 130. 1908. 3. FORBES, S. A. Recent Illinois work on the corn root aphis and the control of its injuries. 111. Agr. Sta. Bui. 178. 1915. 4. GANNON, N., and BIGGER, J. H. The conversion of aldrin and heptachlor to their epoxicides in soils. Jour. Econ. Ent. 51 (1): 1-2. 1958. 5. GRAYSON, J. M., and Poos, F. W. Southern corn rootworm as a pest of pea- nuts. Jour. Econ. Ent. 40 (2) : 251-256. 1947. 6. GREENWOOD, D. E. Wireworm on potatoes. Conn. Agr. Exp. Sta. Bui. 512. 1946. 7. HINDS, W. E. Carbon disulphid as an insecticide. U. S. Dept. Agr., Farmers Bui. 799. 1917. 8. NEWELL, W. Measures suggested against the Argentine ant as a household pest. Jour. Econ. Ent. 2 (5) : 324-332. 1909. 9. SMITH, J. B. The cabbage and onion maggots. N. J. Agr. Exp. Sta. Bui. 200. 1907. 5M 4-59 67655 UNIVERSITY OF ILLINOIS-URBANA