CARBARYL WASHOFF FROM SOYBEAN PLANTS

Both the efficacy and fate of most foliar-applied pesticides may be af fected by weather variables, especially rain. A multiple-intensity rai nfall simulator was used to determine the effects of rainfall intensit y and amount on concentrations of carbaryl (Sevin(R) XLS Plus) washed from soybean plants. Two hours after carbaryl was applied at 1.12 kg/h a, 25 mm of rain was applied at intensities of 13.0, 27.4, 53.8, or 10 5.1 mm/h. About 67% of the carbaryl on the plants was washed off by 25 mm of rain. Rainfall intensity affected carbaryl concentrations in wa shoff; higher concentrations occurred at lower intensities. Even thoug h the experimental conditions were designed for ''worst-case'' conditi ons, washoff patterns suggested improved carbaryl rainfastness when co mpared to carbaryl (formulated as a wettable powder) washoff from cott on plants in earlier studies. Rainfall amount had a greater effect on carbaryl concentrations in washoff than rainfall intensity.