Foliar washoff of pesticides by rainfall

Abstract

Several insecticides were subjected to simulated rainfall after application on octadecylsilanized/trimethylsilanized glass or foliar surfaces. Flucythrinate (cyano(3-phenoxy-phenyl)methyl 4-(difluoromethoxy)-..cap alpha..-(1-methylethyl)-benzeneacetate), fenvalerate ((RS)-cyano(3-phenoxyphenyl)methyl (RS)-4-chloro-..cap alpha..-(1-methylethyl)benzene-acetate), and azinphosmethyl (O,O-dimethyl S-((4-oxo-1,2,3-benzotriazin-3(4H)-yl)-methyl) phosphorodithioate) showed 35-61% washoff by 25 mm of simulated rainfall, while methyl parathion (O,O-dimethyl O-4-nitrophenyl phosphorothioate) loss was over 90% of that applied. Washoff was initially rapid, but reached a secondary slower phase. Chlordimeform (N'-(4-chloro-2-methylphenyl)-N,N-dimethylmethanimidamide) and diazinon (O,O-diethyl O-(6-methyl-2-(1-methylethyl)-4-pyrimidinyl) phosphorothioate), in addition to exhibiting rapid volatilization, suffered nearly complete washoff by 25 mm of simulated rainfall. The use of octadecylsilanized/trimethylsilanized glass slides as a model for cotton leaf surfaces yielded results similar to those seen on actual cotton leaves (Gossypium hirsutum L.). 34 references, 4 tables.