As early as 1912 Headlee compared the relative merits of spraying and dusting in the application of insecticides and concluded that in New Jersey spraying was more effective. By 1914 it had been shown that Bordeaux-arsenical sprays gave potatoes greater freedom front insect and disease Injury than sulfur-arsenical dusts, and thus larger crop yields.
In 1913 C. H. Richardson began investigations of methods of controlling corn earworm. It was found that if a half-and-half mixture of finely divided sulfur and powdered lead arsenate were maintained on the silks from the time the eggs first appeared until harvesting ears, 85 to 90 per cent of the ears would reach market without injury, and that fodder of treated corn could be fed to horses without any ill effects. That the control measure was never generally adopted was probably due to the necessity of applying the treatment before injury became apparent.
About 1919 pink and green aphids were causing considerable damage to potato and tomato crops. Headlee, with the assistance of Rudolfs, undertook the development of nicotine dusts which would kill not only these aphids but also pea aphids, onion thrips, and green peach aphids. Careful studies showed that the nicotine killed by volatilizing as a gas and entering the breathing system of the aphid, but a dust carrier had to be found which would produce prompt volatilization of the nicotine. When subsequently carriers were found and methods of preparing and application of dusts developed, the treatment was widely adopted throughout the United States.
The pepper maggot, an insect native to the horse nettle, became a pest of major importance on this important vegetable crop about 1926. Robert C. Burdette observed in 1928 that when peppers were kept coated with talc dust during the egg-laying period, adult females were unable to grasp the fruit with sufficient strength to drive their eggs through the skin, and in 1929 and 1930 these observations were confirmed by extensive field tests.
In 1930, Burdette turned his attention to other vegetable pests, for example, Mexican bean beetle, corn earworm, and squash vine borer. Rotenone sprays or dusts were found to give outstanding control of the squash vine borer heretofore never held in check. Production of squash and pumpkins became much simpler and more profitable with this control of the borer. Research on these pests was interrupted by the sudden death of Burdette early In 1935. Bailey B. Pepper succeeded Burdette and became department head in 1944, and Clifton A. Wilson front 1946 to 1948 and John P. Reed from 1948 continued work on vegetable insect problems.
Early in the '30s the rigid enforcement of lead and arsenic tolerances by the Federal Food and Drug Administration, including seizures of certain vegetable crops with excessive residues, necessitated a rather intensive search for arsenical substitutes. Early tests with rotenone proved it superior to calcium arsenate and lead arsenate against such pests as Mexican bean beetle, flea beetles, and various caterpillars. Start about 1932, great emphasis was placed on the use of both pyrethrum and rotenone which were found to control a number of vegetable pests and without harmful residues at harvest. At first, costs caused vegetable growers to resist the use of these botanicals, but as the volume of sales increased the price of pyrethrum and rotenone lowered and resistance largely disappeared.
Shortly after 1930 studies of mushroom insects were begun in an effort to help growers in the Landisville and Malaga areas where fungus gnats, manure flies, springtails, and mites were particular factors limiting production. A pyrethrum rotenone, and nicotine dust was developed but it was difficult to find a diluent that would perform with the combination of toxicants. Eventually, it was found that one of the cellite materials was satisfactory for this purpose. This diluent made nicotine, which it fixed rather loosely, available as a contact poison; the rotenone seemed to work as a residual; and the pyrethrum gave a quick knockdown. Supplementary controls through use of nicotine-lime dust and cyanide fumigation were instituted for springtails and mites. When, however, DDT became available in 1945 and experiments showed that a single application of DDT wettable powder to walls of mushroom houses gave insect control for the entire production season, it was believed that the mushroom insect problem was satisfactorily solved. But Pepper was concerned about another mushroom problem. Though as an entomologist he was not primarily concerned with non-insect problems, he had recognized the fungus disease known as bubbles. Subsequently he found that this disease could be prevented by using casing soil which was handled under fallow cultivation during the previous hot summer months.
In the '30s insects which had been known for fifty years or more to be of no economic importance changed their food habits and suddenly caused widespread damage. Sap beetles became important sweet corn pests and increased to the point where now they cause more damage to sweet corn than the European corn borer. The eggplant leaf miner switched from the native nightshade plants to eggplant and in tile late '30s became a serious pest of this vegetable in Salem and Cumberland Counties. Carrot weevil, known earlier as parsley stalk weevil, was not only a serious pest of carrots throughout the state, but also caused serious damage to celery growing in muck soil in the northern part of the state. In this case, the poison bait, a relatively simple control proved effective.
One of the worst pests in the state is the European corn borer. First, in 1935, it was responsible for economic damage to sweet corn in a localized area in Monmouth County. Then in 1936 it spread to Middlesex and Mercer Counties, and by 1939 had spread throughout the sweet-corn-producing areas of the state.
In developing controls for this insect, C. H. Batcheldor of the USDA, Bureau of Entomology and Plant Quarantine, working at New Haven, Connecticut, found that nicotine tannate sprays offered good control. Since, however, New Jersey growers did not have suitable spray equipment, the possible use of insecticidal dust was investigated. Effective control was obtained with 4 per cent actual nicotine added to Wyoming bentonite and fairly effective control resulted from the use of rotenone sprays and dust supplemented with wetting agents. Incidentally, it was discovered that the insecticidal dust also controlled corn smut, a fungus disease. As the program developed a new plant product, ryannia, was discovered by Merck and Company, which in rather low dosages and concentrations, proved to be exceedingly effective against corn borer.
Lettuce yellows, a virus disease transmitted by the six-spotted leafhopper posed another problem. The disease made such inroads that fall production of lettuce was abandoned altogether until It was shown that insecticides could be used as a protection against the sixspotted leafhopper. As a result, in many areas of the state, lettuce is today one of the most important fall crops.
Timothy as a cash crop has disappeared in New Jersey and it is believed that a strong factor in the cause of its disappearance was a mite, new to the United States, which in 1938 was first recorded as doing serious damage to timothy at Freehold, N.J. Although potato tuberworm was another new pest recorded in 1941 as damaging stored seed potatoes in southern New Jersey, after a year or two it disappeared, apparently of its own accord.
In the late '30s when New Jersey adopted a program of marketing potatoes according to U. S. grade, wireworm proved to be a limiting factor in the production of high-grade potatoes. Insecticides such as rotenone, pyrethrum, and nicotine, had been found to be ineffective on such vegetable crops as cabbage, cauliflower, and crops planted in hills because the toxicant was absorbed by the soil and did not reach larvae. However, when studies of new organic fumigants revealed that dichloroethyl ether was a contact poison which would penetrate soil and kill wireworms damaging the roots of plants, growers adopted it for use against wireworms on cabbage, cauliflower, turnips, beets, onions, and other crops. New residual insecticides were later found very satisfactory in killing wireworms, but unfortunately, some of them also affected the soil and consequently the quality of crops grown, particularly root crops. Although seed corn maggot, a companion pest of wireworm, was the cause of serious damage to seeds of beans, peas, corn, and other crops, in recent years protection to the crops has resulted from the use of materials such as lindane, chlordane, dieldrin, and aldrin.
As a result of extensive tests of DDT and other new insecticides, including rhothane, methoxychlor, chlordane, dieldrin, aldrin, heptachlor, parathion, and malathion, on a wide variety of vegetable crops, many were recommended as extremely effective materials. In a few instances use of an insecticide has adversely altered plant growth and quality of the harvested crop. The complicated problem of the effect of insecticides on soil and vegetable quality and flavor has received particular attention from the Entomology Department. Other Experiment Station departments and food processors have been interested in the study, of the problem and have cooperated with the research of the entomologists. In 1954 Billy R. Wilson started studies of ways of removing insects and their eggs from fresh and processed foods.