For more than twenty-five years, Joseph M. Ginsburg has studied the chemical phases of the insecticide problem in the laboratory and in the field. As early as 1930 he showed that oil emulsions and cresylic acid were effective as delayed dormant sprays against apple aphid and European red mite on apple. About the same time he showed that peach trees were less susceptible than apples to injury from refined oil sprays.
Between 1935 and 1942 home-made oil emulsions were studied and several low-cost formulations were recommended to orchardists. Among these oils were several semi-refined oils which were found to be safe on foliage.
Until the appearance of the new synthetic insecticides after the war research on arsenicals received considerable emphasis. About 1930 it was found that hydrated ferric oxide, zinc oxide, and zinc soaps were most effective in eliminating the soluble arsenic which caused foliage injury. Addition of calcium hydroxide to the spray mixture was also found to reduce injury. Studies of compatibility of lead arsenate with fifty salts sometimes present in water used to prepare sprays revealed the danger of using certain types of water in mixing sprays.
From time to time the usefulness of various waxes, spreading agents, and wetting agents in sprays were studied. In 1932, spermaceti, candelilla, or paraffin waxes were shown to reduce spray injury and to act as stickers for insecticides. In 1935 and 1936 studies of surface active agents led to the development of new wetting and spreading agents which could be used safely with nearly all insecticides. In the material-scarce war years, soybean flour was advocated as an efficient spreader, sticker, and emulsifier.
The toxicity of pyrethrum flowers was shown in 1930 to be due to non-volatile pyrethrins rather than to volatile essential oils. The toxicity of derris roots, studied in 1934, was shown to be due in part to other extractives than rotenone. Alcohol and acetone proved to be more efficient than water-insoluble solvents in extracting all toxic ingredients of derris root.
Since 1934, much time has been devoted to studies of methods of analysis for the newer insecticides and assaying residues in and on vegetable, forage, and fruit crops. It has become evident that such factors as dosage and formulation of toxicant applied, rate of toxicant decomposition, mechanical weathering, timing and method of toxicant applications, and plant growth all influence amount of toxicant residues on the plant at harvest. Sprays of organic phosphates have been shown to decompose readily upon application whereas chlorinated hydrocarbon insecticides remain toxic for longer periods. Sunlight is a factor in decomposition.
In the last two years (1952–1954), studies of accumulation of DDT in soils have revealed up to 113 lbs. of DDT per acre in orchards, 35 lbs. in cranberry bogs, and 19 lbs. in crop soils. Practically all DDT was found to be in the upper levels of the soil.