Foliar washoff

Sorption to soil solids and plant cuticular material represents an important process influencing the chemodynamic behavior of insecticides, including their transport in surface runoff Sorption phenomena affect the volatilization, hydrolysis, photolysis and microbial transformation of organophosphorus insecticides. Furthermore, species sorbed to soil particles are transported by erosion processes rather than as solutes in the water phase. Sorption to foliar surfaces reduces the amount of pesticide mobilized by washoff. 

Formulation strongly affects the amount of organophosphorus insecticide washed off from foliar surfaces. For example, azinphos-methyl and phosmet formulated as emulsifiable concentrates were highly susceptible to washoff, while wettable powder formulations were not (58). Thin-walled fenitrothion microcapsules were less prone to washoff than the emulsifiable concentrate (59). The composition of spray adjuvants also affected the degree of washoff (5<5). 

While the occurrence of most processes affecting organophosphorus insecticide concentrations in surface runoff are well documented, many are relatively poorly understood on a mechanistic level. Key processes requiring further study include sorption to plant and soil surfaces, and transfer from soil water into overland flow. Sorption to foliar surfaces determines the amount of applied insecticide available for washoff onto the soil surface or into surface runoff The kinetics of desorption from plant cuticular materials and the effect of adjuvants on foliar sorption processes need additional research. 

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