Disappearance of Spray Deposits of DDT, Methoxychlor, Perthane, Ethion, and Diazinon from Concord Grapes1

Losses of DDT, methoxychlor, and Perthane® (a mixture of diethyl diphenyl diehloroethane (95%) and related reaction products (5%) deposits from the third application of a 3-spray schedule on Concord grapes were measured at biweekly intervals over a period of 42 days. The effects of growth and weathering in reducing the amounts of each insecticide are given separately. Deposits of the three chlorinated hydrocarbon insecticides disappear in the order, from least to most rapid; DDT, methoxychlor, and Perthane. Weathering is primarily responsible for these losses. Reductions in Perthane deposits caused by high temperature were equal to or greater than reductions by rain-fall of 3.11 inches. At harvest the residue of methoxychlor was below the tolerance and usually the combined residues from 2 DDT sprays followed by 1 methoxychlor spray was below the 100% total tolerance for the two insecticides. Reduction in deposits caused by growth and weathering in 4 weeks are presented for diazinon. The effects of growth and weathering on ethion deposits over a period of 4 or more weeks are considered separately. Ethion deposits were more persistent than those of diazinon. When daily temperatures reached a maximum of 90° F. or above, marked and rapid losses in deposits of ethion were found.