AbstractThe insecticide permethrin was applied (10 applications in 6 weeks) to cotton in field plots separated for morning and afternoon applications in early (August to September) and late (September to October) season spray programs. The compartmentalization of permethrin on the leaves was determined throughout the application programs. In each of the four studies, initial surface permethrin residues were 80–90 of the total leaf load. At the end of each study, surface residues had doubled and total leaf content had quadrupled; the surface residues then were 40–45 of the total load. Thus, throughout each phase of the study, a major portion of the leaf permethrin content was at or near the surface where weathering processes occur. The surface residues from the late‐season afternoon applications were generally higher than the residues from the early‐season afternoon applications. This difference was in line with differences in rainfall, temperature and evaporation rates, which favored higher leaf surface residues in the late season. This residue trend did not appear in the morning samples from the two seasons. Thecis:transisomer ratios of the permethrin residues from the late‐season study showed consistently significant decreases, which may have been due in large part tocis‐to‐trans
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