LIBRARY STATE PLANT BOARD June 1949 E-780 United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine DDT SPRAYS FOR CONTROL OF THE CORN EARWORM AND BUDWORM IN SWEET CORN By R. A, Blanchard and W. A. Douglas, Division of Cereal and Forage Insect Investigations, and , G. P. Wene, Texas Agricultural Experiment Station =? The use of sprays for commercial- scale control of the corn earworm ( Eeliothis armigera (Hbn.)) is still in the experimental stage, but a progress report is being given at this time for the benefit of sweet corn growers who may wish to try these methods of control. The methods described are based on experiments conducted in Illinois, Texas, Miss- issippi, and Arkansas during the years 1945 to 1948, inclusive, A large number of insecticides have been tested in sprays and dusts, DDT has given the best control of any that can be purchased on the mar- ket at present, TDE has also given satisfactory control, but is rated as somewhat inferior to DDT on the basis of tests run to date. TDE and other newer insecticides may be found to be equally satisfactory after further tests. In our experiments none of the insecticides have given satisfactory control of heavy earworm infestations when applied as dusts. However, very good control has been obtained with DDT in mineral oil solution and in emulsions containing mineral oil. Application Equipment Four types of equipment for applying the sprays were used success- fully — a knapsack sprayer, a paint-spray machine, and two power sprayers, one with nozzles for hand application and the other with fixed nozzles. Knapsack Sprayer ,— A small knapsack sprayer was used to apply both oil solutions and emulsions to individual ears in small-scale tests. Such a sprayer may be used to treat corn in small fields, but consider- able labor and time are required to keep the spray pressure at the 35 to 40 pounds which seems to be necessary. It is possible to provide the desired pressure by means of a small portable pressure tank such as was used during the war for inflating life rafts. If such a tank is used, the knapsack sprayer should have an air-intake valve welded on it. An air-pressure gage is also necessary to keep from adding more air than the tank will stand. Where it is used to apply emulsions containing oil, l/ Assistance received from D. J. McAlexander, farm manager for F. H, Vahlsing, Inc., Elsa, Tex., and 0, B. Wooten and M, E, Bloodworth, agricultural engineers, respectively, of the Mississippi and Texas Agricultural Experiment Stations, is gratefully acknowledged. JUL - 2 - the liquid must be kept agitated as it is being sprayed; otherwise the oil and water in the emulsion will separate, Paint-Spray Machine ,— Another type of equipment used for applying sprays to individual ears was a small paint-spray machine with a com- pressor run by a gasoline motor. This outfit operated at 30 pounds* pressure breaks up the spray well and drives it into the silk mass. The equipment used in our tests had a quart-size liquid container, but it might be feasible to use a larger machine, having a large liquid con- tainer from which several guns are operated at a time. Some means of agitating the spray, such as a pipe conducting compressed air from the compressor to the bottom of the spray tank, is necessary where an emul- sion containing mineral oil is used. Power Sprayer with Nozzles for Hand Application ,— The spray was applied to th6 individual ears with nozzles attached to hoses on a power sprayer. Each nozzle was equipped with a shut-off valve operated by hand. The spray outfit was mounted on two automobile wheels and was pulled between two rows of corn by a mule. A boom mounted above the corn had outlets for eight 20-foot hoses spaced the same distance apart as the corn rows, so that eight men could spray the ears in eight rows as the machine was pulled through the field. The men walked ahead of the machine, which was operated at a speed slow enough to allow the men to spray each ear. The machine was operated at a pressure of 100 pounds per square inch. About 30 acres per day were treated in this manner. Power Sprayer with Fixed Nozzles ,— Two types of power sprayers with the nozzles mounted in fixed positions were used, a piston-type power sprayer and one employing a gear pump to supply pressure. The piston-type sprayer was suspended between two corn rows belov/ a high- clearance carriage drawn by one mule. The gear pump sprayer was self- propelled, with the pump mounted on a high-clearance detasseling machine. A single gasoline engine served to propel the machine and operate the gear pump for spraying. The type of sprayer is widely used in spraying for chemical control of weeds. Means of agitation are necessary with both machines when emulsions containing mineral oil are to be sprayed. The piston- type sprayer has a mechanical agitator. On the machine employing the gear pump, a hose from the overflow valve on the pump should be run to the bottom of the spray tank. It is very important, in order to prevent clogging, that a strainer of 100-mesh brass or copper wire be fastened on the intake into the pipe line from the tank to the nozzles and that a similar strainer be coupled into this line. The spray nozzles should also be equipped with built-in strainers. In both the machines the spray nozzles were attached to upright supports between the corn rows. There was one of these supports on each side of each row. Two pairs of nozzles, one pair 5 inches above the other, were attached to each support, making four nozzles per row. One nozzle of each pair was directed at a row on either side of the upright. The nozzles were set above the ears, 14 inches from the corn stalks, and were inclined downward to cover the silks and upper parts of the ears with - 3 - spray. The upper nozzle of each pair was directed slightly forward and the lower nozzle of each pair slightly backward. Both machines were operated at 100 pounds' pressure. Kinds of Sprays Suggest For Hand Application to Individual Ears .-- A solution containing 2 pounds of technical DDT in~2~5 gallons of white mineral oil of 50 to 95 seconds Saybolt viscosity can be applied to individual ears with knap- sack sprayers, by men operating nozzles attached to a power sprayer, or with a paint-spray gun. An emulsion made from 3 quarts of factory-pre- pared 25-percent emulsifiable DDT concentrate plus 6 gallons of the above-described white mineral oil. diluted to 25 gallons with water can also be applied in this manner. & The oil and DDT concentrate are mixed together and then stirred into the water until a uniform milky-white liquid is formed. If sufficient agitation is provided by the spray machine, the oil and DDT can be poured directly into the required amount of water in the spray tank. These materials should not be applied until after the ears have been fertilized , i.e ., not until the silks have wilted and begun to turn brown at the ou ter ends . Not more than \ teaspoonful of the oil solution cr i teaspoonful of the emulsion should be applied per ear. Only one application should be made to each ear. The oil solution penetratea the ears better than the emulsion and gives better control of the worms, but will cause some lack of filling at the ear tips. Although the emulsion gives somewhat less control of the 7/orms, the ears will fill out better at the tips. Both will give good control if the materials are carefully applied as soon as possible after the ears are fertilized. A nozzle giving a very fine hollow cone of spray should be used for the hand applications. The angle formed by the cone of spray should not be wider than 50 degrees at 100 pounds* pressure. Otherwise, it will be difficult to get proper coverage of the silks and ear tips. The nozzle should be held 3 or 4 inches above the ear tips and care taken 'to spray" the entire silk" "and" not just one side of the ear^ j No2zLes"~suitabTe for use with a power sprayer are manufactured by several spray-equipment companies, but extreme care should be used to select one that does not put out too large a volume of spray or large droplets. A nozzle with 0.020-inch orifice has been found satisfactory. The nozzle assembly should be equipped with a lever-type shut-off valve that is easy to oper- ate with one hand and has a positive cut-off. The same specifications also apply to the type of paint-spray gun selected, if that method of application is used. 2j Emulsifiable concentrates containing 30 to 34 percent of DDT are also on the market. Five pints of the 30-percent materials or 4Jjr pints of the 34-percent concentrate should be used in 25 gallons of the total spray. The amount of oil remains the same. Hand applications by the above methods of an emulsion containing 10 percent white mineral oil of 50 to 90 seconds Saybolt viscosity will give excellent control _if two properly timed app lic ations are made. The first application should be made before more than 25 percent of the ears are in silk and the second 2 or 3 days late rT~ Experience has~~shown that to determine accurately the percentage of ears in silk actual counts must be made in the field beginning when the first silk appears. The timing will be about right if the first spray applicati on is made one day after an average of 10 percent of the ears are in silk ITs determined by counts made in several places in the field . The g ene r aT~f o rmu la Tor the spray is 3 quarts of 25 percent emulsifiable DDT concentrate plus 2^ gallons of white mineral oil diluted to 25 gallons with water. Ears that have silks as well as shoots which have not yet developed silks should receive the spray application. The knapsack sprayer, paint-spray gun and power sprayer have all been used successfully for applying the emulsion containing 10 percent mineral oil. For Power Application from Nozzles in Fixed Positions ,— Tests in- dicate that the emulsion containing 10 percent of white~mTneral oil of 50 to 90 seconds Saybolt viscosity is best for applications from nozzles in fixed positions. With this type of equipment two applications should be made on a carefully planned schedule. If care is exercised to see that not over 10 percent of mineral oil is put into the spray, no damage to the corn should resxilt. This is true whether the material is applied from fixed nozzles on a power sprayer or by hand applications from a knapsack sprayer, paint-spray gun or from hand nozzles attached to a power sprayer. The general formula for such a spray is the same as for the hand applications mentioned above: 3 quarts of 25 percent emulsifi- able DDT ■=/ concentrate plus 2^- gallons of white mineral oil diluted to 25 gallons with water, & Approximately 25 gallons per acre per applica- tion should be applied. Spray nozzles with 0,026-inch orifice giving a flat fan-shaped spray gave excellent results in 1948. However, a nozzle putting out an equal amount of spray in the form of a hollow cone might be equally effective. The angle formed by the spray as it comes from the nozzle should not be over 50 degrees at 100 pounds' pressure. If the spray comes out at too wide an angle p it will cover too much of the "pl&rvt * thereby lessening th e amount reaching the ears . Fixed Nozzle Spraying for Control of Budworms ,— The earworm and the fall armyworm ( Laphygma frugiperda (A.& Sj) often attack sweet corn before and during tassel formation. When they infest corn in this way, they are commonly called budworms. They may injure the plants severely, and the large larvae may later travel from the tassels to attack the young ears. It was found that a single application of emulsion containing DDT and 5 percent of mineral oil would effectively control such worms. The material can be applied with a machine on which the nozzles are held in a fixed position somewhat as already described. However, two nozzles should be set directly above the plants to shoot downward, and two should be directed at the ear-bearing sections of the plants, A single nozzle fixed directly above the plant and one fixed on each side might be suf- ficient to give control. The formula recommended is 3 quarts of 25- - 5 - percent emulsif iable DDT concentrate & and 10 pints of white mineral oil of 50 to 95 seconds Saybolt viscosity, diluted to 25 gallons with water. A single application made just as damage begins to be general over the field should protect the plants and young ears from damage. This spray application will not protect the ears after they begin to silk ; therefore , the single or double applications suggested previously for control of the earworm infestation should be made at the proper time . Discussion and Precautions The effects on the plants and ears of the materials tested and methods of applying them have been 'carefully studied. No bad odor or taste has been detected in repeated trials of sweet corn that had been treated with the sprays and by the methods described in this paper. Fur- thermore, no evidence has been found that any of the materials or methods of application recommended were detrimental to the corn except for some failure of tip kernels to fill out when an oil solution of DDT was used. However, it should be pointed out that the materials and methods recom- mended have not been widely used by growers and should be used with caution. The strengths of the formulations and the dosages recommended should not be exceeded, for to do so may result in damage to the corn . Emulsif iable DDT concentrates with strong disagreeable odors should be avoided. Under no conditions should kerosene or an oil with a kerosene odor be used. A considerable number of samples of the corn that had been treated with the insecticides suggested in this paper have been analyzed for the presence of DDT residues. These analyses have shown that the husked ears are entirely safe for use as food, but that appreciable residues of DDT may be present on the husks, silks, leaves, and stalks , Although these residues are not likely to cause acute poisoning of livestock to which the plants are fed, very small quantities of DDT may be secreted in the milk and the fatty tissues of such animals. Therefore , the treat ed plants should not be fed to dairy animals or to meat animals that are being finished for slaughter . UNIVERSITY OF FLORIDA 3 1262 09239 2009