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.