L STATE PLANT BOARE. March I9U5 E-6U0 United States Department of Agriculture ■ • Agricultural Research Administration Bureau of Entomology and Plant Quarantine EXPERIMENTS WITH DDT FOR CONTROL OF INSECTS ATTACKING CEREAL AND FORAGE CROPS IN THE FIELD' AND IN STORAGE Compiled "by C. M. Packard Division of Cereal and Forage Insect Investigations Experiments conducted v/ith DDT (l-trichloro-2,2-bis(p-chlorophenyl) ethane) during I9UH. for the control of various insects that attack cereal and forage crops in the field, and grains, seeds, and milled cereal products in storage, are "briefly summarized in this paper. In considering these results it should he clearly understood that no recommendations are "being made for the practical use of DDT on any of these crops or against any of these insects. Many questions remain unanswered relative to "best mixtures or solutions to use, dosages to apply, application schedules, residue. hazards, effects on "beneficial insects, and results when used under conditions different from those prevailing in this year*s experiments. Further investigations are necessary in order to ohtain the answers to these Questions, Grasshoppers In field trials "by J. R. Parker, E. J. Hinman, and C. C. Wilson, various. concentrations and dosages of DDT in pyrophyllite , were applied as dusts to alfalfa and range grasses in Arizona, California, and Wyoming, The results indicated that very high mortality of grasshop- pers, including Melanoplus mexicanus (Sauss,), M, "bivitattus (Say), M. fcmur-rubrum (Deg.) , and Camnula pellucida (Scudd.) , can "be obtained from a single treatment with 15 to 20 pounds per acre of dusts contain- ing 15 to 20 percent of DDT. Good control was also obtained with sprays made from a dust containing 10 percent of DDT in pyrophyllite mixed v/ith water to give O.36 to 0.U8 percent of DDT. The results of very limited trials of an aerosol containing 3 percent of DDT and 1,5 percent of pyrethrum extract were inconclusive. Fair to good mortality of grasshoppers was obtained by Mr, Wilson from a single application, at the rate of about 20 pounds per acre, of a bait mixture containing the follov/ing proportions! 3 pounds of pow- dered technical DDT, 100 pounds of wheat bran, 1 gallon of molasses, and 1-1/2 gallons of water. -2 ~ Chinch Bug In field tests conducted "by P. Lugihbill and C. Benton near Lafayette, Ind. , barrier lines of dust containing 5 percent or more of DDT in pyrophyllite, applied at the rate of ahout 1 pound per rod, gave excellent protection of corn from immature chinch hugs ( Blissus leucopterus (Say)) migrating to it on foot from adjacent wheat. The dust did not act as a repellent or prevent some of the hugs from reaching the corn, hut it killed them. hef ore they were ahle to injure the corn materially. Dusts containing lower percentages of DDT were not tested hut may "be found effective. Heavy applications of dusts containing 1 to 5 percent of DDT in pyrophyllite directly to the infested portions of the corn plants and the surface of the soil close to them gave excellent control of the "bugs without discernihle injury to the plants* Lygus Bugs Attacking Seed Alfalfa In control experiments with Lygu s spp, conducted "by F, V, Lieherman on seed alfalfa at G-andy, Utah, one application of a pyrophyllite dust containing 10 percent of DDT at 27-jj pounds per acre of the dust produced 135 to 725 pounds of thresher- run seed per acre, with an average of U28 pounds as compared with practically complete loss of the seed crop in undusted areas. The seed matured earlier in the DDT-treated plots and was riper and cleaner than that produced in plots treated with other insecticides. Owing to an early frost, seed from most of the plots treated with other insecticides was "badly hlackened and all seed in them that might have matured in the cocks was shriveled. The results were affected, however, by uneven soil moisture, in the various plots and the ahnormally early frost, so that the comparative effectiveness of the different treatments could hot he closely evaluated. The DDT was" applied during the pre-hloom stage after the "buds had formed "but "before many flowers had opened, in order to avoid killing wild "bees essential to" pollination. No domestic "bees were present in the area. So far as could be observed the DDT had no repellent effect on, and caused no mortality of, the wild "bees. .The experiments indicated the possihili»ty'that DDT can be used without appreciable harm to domes- tic or wild hefts. provided application during the main "blooming period is avoided, but further observations are necessary for the settlement •f this question-., Largo aphid and thrips populations in the treated plots were virtually eliminated* .Other insects, such as coccinellid "beetles and larvae', nabid nymphs and adults, grasshoppers, flies, and lepidopterous larvae, were killed. The highly migratory species constantly reinfested the plots, but their numbers were usually less in DDT-treated than in untreated plots, indicating that this insecticide has a lasting residual effect. - 3 - Vetch Bruchid Field experiments near Oregon City and Dayton, Ore., indicated DDT to be very promising for the control of the vetch bruchid ( Bruchus brachial is Fahraeus) attacking hairy vetch seed, L. P. Rockwood and M, M, Heeher found that on hairy vetch two applications of a dust con- taining 5 percent of DDT in pyrophyllite, at rates of 22 to 25 .pounds of the dust per acre as the pods began to set and 15 days later, gave .excellent control -o>f the vetch bruchid without visible injury to the plants,- and were significantly better than two applications of a dust containing 1 percent of rotenone at approximately the same rates per acre. The DDT remained effective much longer than the rotenone, and it seemed probable that three or four applications of the latter would have been necessary to equal two applications of the DDT in effective— ness« A single application of a dust containing 3 percent of DDT in pyrophyllite, at the rate of 22 to 25 pounds per acre applied 10 days too late for best results on 5 acres of hairy vetch at Dayton gave commercially profitable although not full control. The season* s results indicate that one well-timed application of 3 percent DDT dust at 25 to 35 pounds per acre may give adequate control of the vetch bruchid. Several other species of insects, including coccinellid beetles, were killed by the DDT, and also by the rotenone dust and by an arsenical bait spray that was being tested. Very few aphids and no syrphid or coccinellid larvae appeared to have been affected. No dead bees were found nor could any decrease be noted in the number of live honeybees swept from the dusted plots. Bees may be an aid to good pollination of hairy vetch, however, and more conclusive observa- tions are necessary to determine what effect the application of DDT to this crop may have on them. Velvetbean Caterpillar Excellent control of the velvetbean caterpillar ( Anticarsia gemmatilis (Hbn.)) on peanuts and soybeans .was obtained by H c C. Young, of this Bureau, and L. L. English, of the Alabama State Agricultural Experiment Station, in field tests with single applications of DDT dusts and sprays. A dust containing 3 percent of DDT in pyrophyllite was effective and the results indicated that more dilute dusts might also be satisfactory. Further information is needed to determine the best dust and spray preparations and dosages to apply for control of this insect. Mr, Young observed that the residue of several applica- tions of a concentrated DDT spray, obtained by mixing 10 percent DDT- pyrophyllite dust in water containing a small ocrcentage of spreader, to peanuts in July, for control of the white-fringed beetle, was effec- tive against an infestation by the velvetbean caterpillar which devel- oped in mid-September. - u- Potato Leafhopper on Alfalfa and Peanuts At Beltsville, Ml. , P. W. Poos obtained a great reduction in numbers of the potato leafhopper ( Empoasca fabae (Harr.)) on alfalfa and peanuts "by two -applications 9 days apart of a dust containing 2 percent of DDT in pyrophyllite, or of a spray consisting of a mixture of 0.66 percent of DDT in dust form with water, with a spreader added. • Material increase in yield and quality of hay was obtained in the treated alfalfa plots. Two applications l6 days apart of the same spray and dust to peanuts resulted in great reduction of the leafhop- per population but no increase in yield because of severe leaf spot infection on both treated and untreated plots late in the season. Tobacco Thrips on Peanuts Observations and experiments by P. W. Poos, at Beltsville, lid., have indicated that the tobacco . thrips ( Prankliniella fusca (Hinds)) is the chief cause of the widespread injury to young peanut plants commonly known as pouts. In an effort to determine primarily how much effect this injury has on yields, seven applications of 2 per- cent DDT-pyrophyllite dust, were, made at J- to 2-day intervals to one series of plots, 8 applications at U- to 6-day intervals of a spray containing 0.66 percent of DDT, obtained by mixing a 10 percent DDT- pyrophyllite dust v/ith water and a small percentage of spreader, to another series, and 8 applications at H- to 6-day intervals of an aerosol containing 10 percent of DDT to a third series. Good control of the thrips and decided increases in yield resulted from all these treatments, with no evidence of injury to the plants. European Corn Borer in Sweet Corn Following favorable results from preliminary trials of DDT by D. D. Quest el in 19^+3 for the control of the European corn borer ( Pyrausta nubilalis (Hbn. )) in sweet corn, experiments were continued in l^kk near Toledo, Ohio. In field-plot tests conducted by C. H. Batchelder, in which different strengths and dosages of DDT in pyrophyl- lite were applied with ground equipment, borer reductions of J2 to 91 percent were obtained by four applications at 5- to* J-iay intervals of dusts containing 3 to 6 percent of DDT, at 1.2 to 2.U pounds of DDT per acre-application. Pour aerial applications at 3~ to 5*"&ay intervals of a dust mixture of 3 • 75 percent DDT in pyrophyllite, at approximately 1.5 pounds of DDT per acre-application, gave borer reductions of 7*+ percent in the plants and 82 percent in the ears. Excellent control was obtained on the sweet corn variety Evergreen from four aerial applications at 3- to 5-cLay intervals of a concentrated spray contain- ing 8.9 percent of DDT dissolved in a horticultural oil, at the rate of about 2 pounds of DDT per acre-application. - 5 ~ Three applications at 5-day intervals of sprays containing approximately 0.05 percent of DDT were made "by Mr. ?uestel in another series «f pltts, at the rate of O.76 pound »f DDT per acre-application. These sprays "/ere made "by mixing a pyrophyllite dust containing 10 per- cent of DDT with water and a small percentage of spreader. The treat- ments resulted in 92 to 98 percent reductions in numbers of borers in the plants as compared with the populations in check areas. Corn Earworm in Sweet and Seed Corn Injection of white mineral oil containing 1 percent or more of DDT into the silks of sv/eet corn ears produced 85 to 99 percent of worm-free ears, in experiments conducted by J. T7ilc«x, of the Division of Truck Crop and Garden Insect Investigations in southern California fields heavily infested with the corn earworm ( Heliothis armigera (Hbn.)) A variety »f oil solutions and emulsions of DDT in concentrations of 0.5 to 2 percent were tested by H. A. 3 lane hard in Illinois on ears of sweet corn and on dent corn grown for seed, by injection into the silks and atomization on them, for the control of the earworm* From 91 to 100 percent of worm- free ears were obtained by either injection or atomization of 2 percent of DDT in undiluted white mineral oil. Various degrees of control were obtained with the different emulsions. The results indicate that one may be found that will give high protection from the earworm when it is atomized on the ears, at comparatively low cost and with.no injury to the ears or plants. Corn Flea Beetle Good protection of young sweet corn from the corn flea beetle ( Chaetognema ' pulicaria Melsh.) and considerable reduction in the bacterial wilt which it transmits were obtained in experimental plots of a wilt- susceptible and a wilt-resistant variety conducted by F. ~. Foos at Beltsville, Md. Following 5 applications of 0.66 percent DDT spray, obtained by adding 10 percent DDT-pyrophyllite dust to water containing a small percentage of spreader, at intervals of 3 tc 6 days, only 2 beetles were found on a treated row rf corn as compared with 128 on an untreated row. In the susceptible variety a much better stand was main- tained in the treated rows than in the untreated revs. White-fringed Beetle The high effectiveness- of DDT. obtained in rtreliminary tests by H. C. Young and staff during I9U3, both as a stomach and' a contact poison for the white-f ringed beetle ( Pantomorus leucoloma . (Boh. ) ) , was substan- tiated by various experiments carried; on by them at Florala, Ala.., in 19HU. In these tests a. dust containinglO percent of DDT in pyrophyllite was used in the preparation of all dusts, sprays, and soil treatments. - 6 Sprays containing 1/8 pound or more of DDT and 0.1 pound of a wetting agent per 100 gallons of water, applied to peanut and chrysan- themum foliage as a stomach poison, gave mortalities of adult "beetles in excess of 90 percent, and were as effective as a spray containing 8 pounds of synthetic cryolite (approximately JO?? sodium fluoaluminate) and 0.1 pound of wetting agent per 100 gallons of water. Sprays con- taining 1/2 pound of DDT in dust form per 100 gallons of water with wetting agent gave an average mortality of 93 percent of adults when applied as a contact poison, DDT dusts applied as a contact poison against the adults of the white-fringed "beetle showed' that lighter dosages gave greater mortali- ties when applied to the surface of the soil on which the "beetles crawled than when applied to the beetles themselves. Heavier dosages were more effective when applied to the "beetles. ?yrophyllite dust containing 5 percent of DDT applied to -the "beetles and on the soil at the rate of 0.77*+ pound of DDT per acre gave 38 .percent mortality. The fact that DDT applied to the surface of the soil is effective as a contact poison against the adults is considered the most important finding of the I9UU season. DDT dusts applied to the foliage remained effective against adults for. ah out, 5 days or until' 0.25 to 0.50 inch of rain had fallen. When no rain fell, the dusts gave fair mortality for more than 5 days. A dilute spray containing 0.2 pound of DDT, 2 pints of fish oil, and 0.1 pound of a wetting agent per 100 gallons of water remained effective for ahout 10 days* A concentrated spray containing h pounds of DDT, 20 pints of fish oil, and l,lU pounds of a wetting agent per 100 gallons of water gave an average mortality of 66 percent after 10 days' exposure and 5»°7 inches of rain, and 56 percent after 15 days' exposure and 7*95 inches of rain. When mixed with the top 3 inches of soil, DDT at 5^ and 100 pounds per acre caused mortalities of 3^ and 65 percent of the adults, respec- tively, by the end of 7 days., in field cages, containing potted chrysan- themum plants in untreated S:oil as food. ' .'./, ■ : > In laboratory tests DDT applied .to soil at rates of 25 to 250 pounds. per acre gave mortalities of larvae in- the soilvof from 35 to 100 percent. -It was more effective against half-grown than against larger larvae. Lead arsenate similarly tested at the rate of 1,000 pounds per acre did not cause any mortality, while DDT at 5° pounds par acre gave 95 percent mortality of half-grown larvae during the 3°~day test period. In small salve-box tests of baits against three-fourths grown larvae in moist sterile soil, peanut meal containing 10 percent of DDT caused 50 percent mortality in 15 days, while ground whole peanuts con- taining 1 and 5 percent of DDT caused 95 and 100 percent mortality, respectively, in 15 days. » • DDT'used in a water suspension did not kill the eggs of the white- fringed beetle, but when dissolved in kerosene at rates of 1.6 to 6.U. grams per 100 ml. it was an effective ovicide. •" - 7 - Radishes grovm in soil' containing 250 pounds of DDT per acre, thoroughly washed, and then fed to three-fourths grown larvae caused no mortality in 33