LIBRARY STATE PLANT BOARD July 1950 E-780, revised United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine DDT SPRATS FOR CONTROL OP THE CORN EARWORM AND THE BUDVORM IK SWEET CORN By R. A. Blanchard and W. A. Douglas, Division of Cereal and Forage Insect Investigations, G. P. Wene, Texas Agricultural Experiment Station, and 0. B. Wooten, Bureau of Plant Industry, Soils, and Agricultural Engineering and also of Mississippi Agricultural Experiment Station 1/ The use of sprays for commercial- scale control of the corn earworm ( Hellothls armlgera (Hbn.))is still in the experimental, stage, but has been successful in a number of places. The methods here described are based on experiments conducted in Illinois, Indiana, Mississippi, Missouri, and Texas during the years 19^5 to 19^9 » inclusive. Many insecticides have been tested in sprays and dusts, and DDT has given the best control. TDE has also given fairly satisfactory control, but is rated as somewhat Inferior to DDT on the basis of tests that have been run. TDE and other never insecticides may be found after further tests to be as satisfactory as DDT. Hone of the insecti- cides tested 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 emulsions. Equipment Four type 8 of equipment for applying the sprays were used suc- cessfully — a knapsack sprayer, a paint-spray machine, and two power sprayers, one with norzles 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 considerable labor and time are required to keep the spray pressure at the Uo to 1*5 pounds which seems to be necessary. It is possible to provide the desired pressure by means of a small portable pressure 1/ D. J.. McAlexander, Farm Manager for F. H. Yahlsing, Inc., Slsa, Tex., assisted in these studies. - 2 - 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 and to be sure that the proper pressure is maintained. Where this type of sprayer is used to apply an emulsion containing oil, the liquid must ha kept agitated by occasional shaking 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 compressor run by a gasoline motor. This outfit, operated at a pressure of 30 pounds per square inch, breaks up the spray well and drives it into the silk mass. The equipment used in our tests had a 1-quart liquid container, but it might be feasible to use a machine having a large liquid container from which several guns are operated at the same time. Some means of agitating the spray, such as a pipe to conduct compressed air from the compressor to the bottom of the spray tank, is necessary where an emulsion containing mineral oil is used. Power Sprayer with Bossies for Hand Application .— Both oil solutions and emulsions have been successfully applied to the individual ears with nossles 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 by a mule between two rows of corn. 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 them to spray each ear. The sprayer was operated at a pressure of 100 pounds per square inch. About 30 acres per day were treated in this manner. Power Sprayers with Tlxed Bossies .-— Two types of power sprayers with the nossles mounted in fixed positions have been used — piston- type pump on one and on the other a gear-pump to supply pressure. The spray rig employing the piston pump was suspended between two corn rows below a high clearance carriage and was drawn by one mule. Several spray rigs using gear pumps were used in different areas. They were all self- propelled with the spray outfit mounted on a high-clearance corn- detasseling machine. Ob one rig using a gear pump, an air-cooled gaso- line engine drove the machine and also operated the pump for spraying. A second rig of this type had an automobile engine mounted on a detasseling machine. In a third self-propelled rig the power unit was a small tractor with the chassis raised above the wheels to obtain the necessary clearance. The rear wheels were driven from the rear axles by roller chains. This type used a gear pump to supply pressure. Xither a piston-type pump or a gear-type pump such as is widely used on weed sprayers could be used with the two last-named power units* - 3 - Means of agitation are necessary when enulsions containing mineral oil are to be sprayed. A mechanical agitator in the spray tank is best, and power sprayers with pis ton- type pumps are usually so equipped. Where an automobile engine or small tractor is used to supply power, an agitator can easily be arranged to work with the gear pump. This may be somewhat more difficult where the spray rig is propelled by an air-cooled engine driving the front wheel. Some agitation may be provided by a hose from a bypass valve connected between the bottom of the tank and the pump, but such an arrangement may not be very satis- factory if the spray tank is large. One spray rig used in I9U9 had a large air-cooled engine to drive the front wheel and a smaller engine mounted on the tank to drive the pump and agitator. To obtain satisfactory results the pump used must be large enough to provide adequate pressure for the number of rows it is desired to spray at one time. The manufacturers of the low-gallonage nozzles rate the output in gallons per minute or gallons per hour. The pump should have sufficient capacity to carry the combined output of all the largest nozzles to be used on the rig at l^O pounds per square inch. To prevent clogging, it is important that a strainer of 80- to 100-mesh brass or copper wire be fastened over the opening from the spray tank into the supply line and that a similar strainer be coupled into the line between the pump and the nozzles. Th* strainers, especially the one between the pump and nozzles, should be large enough to allow unrestricted flow of the maximum amount of spray required for the number of nozzles in use. Otherwise the required nozzle pressure cannot be maintained. Use of a line strainer of insufficient capacity was one of the principal difficulties with the first large sprayers tested. The drops carrying the spray nozzles can be attached to the boom in at least two different ways (fig. 1), as follows: (1) The supply hose to the individual drops can be either screwed Into the boom or can be supplied from a smaller manifold attached to the boom. The drop may be rigid (fig. 1, A), with vertical adjustment of the nozzles being made by raising and lowering the drop/ which is held in place by a set screw. (2) a drop-pipe (fig. 1, B), which is semirigid. A short piece of hoee is used to reduce vibration. The pipe is held in a straight line with the row by clamping it to a piece of strap iron as shown. Vertical adjustment of this type of drop is accomplished by raising and lowering the boom. The drops in both types are suspended midway between the rows and the attaching parts are welded to the boom if fixed row widths are used. If the row widths are to be varied, as in cases where other crops are to be sprayed, a clamp may be devised for attaching the drops to the boom. This will allow changing of row widths. The nozzle cluster for both types of drops is shown in figure 2. - 1* - Two pairs of nozzles, one pair 5 inches above the other, can he attached to each drop, making four nozzles per row* One nozzle of each pair Is directed at a row on either side of the drop. The nozzles should he set above the ears, about lU Inches from the cornstalks, and Inclined downward to cover the silks and upper parts of the ears with spray. Equally good results have been obtained with nozzles putting out a flat- fan-shaped spray and ones with a hollow-cone- type spray, provided the output of each type is the same. In case of the flat-fan type, the upper nozzle on each side of the row can be directed forward and in toward the row at about a 45-degree angle and the lower one on each side backward and in at about 45 degrees. The nozzles should be adjusted so that the fan of spray is spread vertically, not horizontally. Apparently the best results with the hollow-cone-type nozzles are obtained when the two nozzles on each side of the row are aimed directly at each other or the upper ones slightly forward and the lower ones slightly backward. The machine should be operated at a minimum pressure of 100 pounds per square inch, and in experiments in I9H9 increasing the pressure to I5O pounds increased the effectiveness of the spray* Kinds of Sprays Suggested Tormulations for Single Hand Application to Individual liars .— A solution containing 1§ pounds of technical DDT in 25 gallons of white mineral oil of 65 to 95 seconds Saybolt viscosity can be applied to individual ears with knapsack sprayers or by men operating nozzles attached to a power sprayer, or with a paint-spray gun. This solution should not be applied until after the ears have been fertilized , i.e. . not until the silks have wilted and began to turn brown at the outer ends . An emulsion made from 3 quarts of factory-prepared 25-percent DDT emulsif iable 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 the DDT can be poured directly into the required amount of water in the spray tank. This emulsion should be applied as soon as 90 to 100 percent of the ears are in silk. A single application made at that time will not injure the ears. Not more than £ teaspoonful of the oil solution or \ teaspoonful of the emulsion should be applied per ear. Only one application should be made to each ear. The oil solution penetrates the ears better than the emulsion and may give slightly better control of the worms, but will prevent the filling out of kernels at the ear tips. Although the emulsion gives a somewhat lower kill of the worms, the ears will fill out better 2/Emuls if lable concentrates containing 30 to 34 percent of DDT are also on the market. Five pints of the 30-percent concentrate or k% pints of the 34-percent concentrate should be used in 25 gallons of the spray. The amount of oil remains the same. - 5 - at the tips. Zither formulation will give good control if applied as recommended. A nozzle giving a rery 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 1 pressure. Otherwise, it will be difficult to get proper coverage of the silks and ear tips. The nozzle should be held 3 or ^ inches above the ear tips and care taken to spray the entire silk and not just one side of the ear. Nozzles suitable 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 too large droplets. Nozzles with capacities at 100 pounds 1 pressure of 1.5 gallons per hour where the oil solution was used and 2.5 gallons where the emulsion was used were found satisfactory. The nozzle assembly should be equipped with a lever-type shut-off valve that is easy to operate 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. These sprays are not recommended for application by machines with fixed nozzles because of cost of the spray and the difficulty of getting good control with only one application. Formulations for Two or Three Hand Applications . — Hand applications by the methods just discussed of an emulsion containing 10 percent white mineral oil of 65 to 90 seconds Saybolt viscosity will give excellent control if two properly timed applications are made. The first application should be made 1 day after 7 to 10 percent of the ears are in silk and the second 2 or 3 days later. Xxperlence 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 general formula for the spray is 3 quarts of 25-percent DDT emulsifiable concentrate plus 2\ gallons of white mineral oil diluted to 25 gallons with water. Because of the presence of the oil , this emulsion must be stirred up well and must likewise be shaken periodically or otherwise kept agitated as JL£ is_ being applied . Bars that have silks, as well as shoots on which the silks have not yet developed, should be sprayed. The knapsack sprayer, paint-spray gun, and power sprayer have all been used successfully for applying the emulsion containing 10 percent mineral oil. With the knapsack sprayer, however, it is important not to let the pressure drop below kO pounds. Power Application from Nozzles in Fixed Positions . — Tests in a number of areas have indicated that an emulsion containing 5 or 10 percent of white mineral oil of 65 to 90 seconds Saybolt viscosity is best for applications from nozzles in fixed positions. Two or three properly timed applications should be made. Two applications have given good control, but the percent of worm-free ears was somewhat greater where three applications were made. The third application gives added assurance of a high percentage of perfect ears. If three applications are made the oil in the emulsion may be reduced to 5 percent. Where three applications are planned, the first should be made - 6- 1 day after the first silks appear and the second and third applications at intervals of 2 days. Where two applications are planned, the first should he made 1 day after 7 to 10 percent of the ears are in silk and the second after an interval of 2 or 3 days. The general formula for the sprays where two machine applications are to be made is the same as for the two hand applications already mentioned — 3 quarts of 25 percent emulsif iable DDT 2/ concentrate plus 2£ gallons of white mineral oil diluted to 25 gallons with water. If three applications are to be made the formula is the same, except that the oil in the emulsion may be reduced to l£ gallons. 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 result. This is true whether two or three applications of the material are made from fixed nozzles on a power sprayer or two applications from a knapsack sprayer, paint-spray gun, or hand nozzles attached to a power sprayer. ]J JL minimum of 25 gallons per acre per application should be used. Spray nozzles with an output of 8 to 9 gallons per hour each at 100 pounds* pressure have given excellent results where the machine was operated at a speed between 3 and 3^ miles per hour. For operation at higher speeds correspondingly larger nozzles should be used. Hozsles of the same output capacity giving either a flat-fan or hollow-cone- shaped spray pattern have given equally good results. The angle formed by the spray as it comes from the nozzle should not be over 6o° at 100 pounds' pressure. If the spray comes out at too wide an angle, it will cover too much of the plant, thereby lessening the amount reaching the ears. Fixed Kozzle Spraying for Bud worm Control .— The earworm and the fall armyworm ( Laphygma frugiperda (A. and 8.)) 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 noszle 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 23-percent DDT emulsif iable concentrate j~/ and l£ gallons of white mineral oil of 65 to 95 seconds Saybolt viscosity, diluted to 25 gallons ^/Country Gentleman hybrids appear to be more susceptible to injury from DDT emulsions applied by hand than are other hybrids. - 7 - with water. A single application made just as the damage begins to be general over the field should protect the plants and young ears from damage. In most instances this spray application will not protect the ears after they begin to silk but, if damage does not become too severe in the field before silks begin to emerge. two or three regular earworm sprays designed for protection of the ears will also kill larvae migrating from the tassels to attack the ears. Factors Influencing the Effectiveness of Control Measures Even with the most severe infestations observed to date, 85 to 100 -percent of marketable ears can be expected from any of the treatments outlined, if properly applied and timed. This high percentage of control has been obtained in fields where 35 percent or more of the ears in untreated checks have been unmarketable. Up to 90 percent of worm-free ears have been obtained in very severely infested commercial fields under certain conditions. Some of the conditions known to affect the percentage of worm-free ears are given below. Type of Hybrid . — Hybrids with open growth and few tillers facilitate spraying of the ears properly, either by hand or machine. Conversely, hybrids that have a bushy type of growth with many tillers make it difficult to obtain a high percentage of worm- free ears. Hybrids that are less injured by earworms because of relatively long, tight husks, or for other reasons, are easier to protect from earworm damage than are those more subject to severe injury. Rate of Planting . — Earworm control by any method will be diffi- cult if plants are too close together in the row in drilled corn or if there are too many plants per hill where corn is planted in checkrows. Actual data on the effect of spacing on control are not available, but it is known that the percentage of control is reduced if plants are less than 10 inches apart in drilled fields, or where there are more than 3 or U plants per hill in checkrowed corn. Under most conditions the number and site of ears are seriously reduced by close planting. Excessively thick planting is thus a source of loss rather than profit. Spacing of Corn R o ws .— If it is planned to spray corn by a machine with fixed nozzles, particular care should be taken to space the rows uniformly when it is planted. If the spaces between rows vary greatly, the nozzles on each side of some rows will not be at the right distance from them for best results. Discussion and Precautions The effects on the plants and on the ears of the materials tested and the 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 thi6 paper. Furthermore, no evidence has been found that any of the materials or methods of application recommended were detrimental to the corn, except - 8 - for some failure of tip kernels to fill out when an oil solution of DDT was used. However, the materials and methods recommended should he used with caution. The strengths of the formulations and the dosages recommended should not he exceeded, for otherwise the corn may he damaged. Bmulsifiable DDT concentrates with strong odors should he avoided. Under no conditions should kerosene or an oil with a kerosene odor he used. ▲ considerable number of samples of the corn that had heen treated with the insecticides suggested in this paper have heen analyzed for the presence of DDT residues. These analyses have shown that the husked ears are entirely safe for use as food, hut that appreciable residues of DDT may he 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 absorbed into the fatty tissues of such animals. Therefore , the treated plants should not be fed to dairy animals or to meat animals that are being finished for slaughter . f\ PQ [ W CO o nflu Hgp CO CO 1 ft I U ft Digitized by the Internet Archive in 2013 http://archive.org/details/spracontOOunit SWIVEL NOZZLE SUPPLY HOSE 0?. DROP PIPE CROSS 40" row 12" to H» 36" row S" to 10" 30" row 2" to 4" Figure 2. — Nozzle Cluster. UNIVERSITY OF FLORIDA lUllllllflWUIlllllllllill 3 1262 09239 2306