Post-application slough-off of pesticide deposits on orange trees.

Abstract

Toxicant loss from fruit and leaf surfaces after a pesticide application was considered by GUNTHER and BLINN (1955) to be composed of 3 separate steps. The first step, occurring immediately after the pesticide spray had dried, was postulated to be a rapid loss within a few hours to a few days of the loosely adhering deposits consisting of pesticide sorbed to formulation carrier and to natural dust on the plant. The following step was a dissipation of toxicant from the more tenaciously adhering deposits through volatilization and decomposition of the compound by the action of sunlight and moisture. The duration of this step could be several days to several weeks. The final step was dissipation of the residues at a greatly reduced rate through a combined action of dislodgment, volatilization, chemical degradation, and penetration into subsurface tissues. The occurrence of the second and final steps, designated on semi-logarithmic plots of pesticide dissipation as the degradation and persistence curves, respectively, was reviewed by GUNTHER (1969) for about 40 insecticides and acaricides on citrus fruit. WESTLAKE et al. (1973) demonstrated this phenomenon on both citrus fruit and foliage for the newer insecticide dioxathion. Much interest has been currently generated with respect to foliar residues because of the current belated emphasis on worker safety in pesticide-treated groves. The visible accumulation of dust on foliage has been recorded by many workers