MODELING INSECTICIDE RESIDUES ON KIWIFRUIT FOLIAGE - EFFECT OF RESIDUE AGE ON INSECTICIDE ACTIVITY AND CONCENTRATION

Chlorpyrifos EC was applied at a range of rates to kiwifruit leaves in an experiment designed to test the adequacy of a published residue de cay and activity model for the case of insecticide on kiwifruit. Treat ed leaves were sampled over a period of 51 days following spray applic ation, with residue levels determined by chemical assay, and residue t oxicity to lightbrown apple moth Epiphyas postivittana assessed by bio assay and logit regression analysis. Residue activity indexed as the r esidue level for 90% mortality (LR90) was shown to decline substantial ly as residues aged from 2 to 51 days. A log residue-log time model wa s shown to be a more robust representation of residue decay characteri stics than the exponential model frequently used.