Residual toxicity studies conducted during 1995 indicated that imidacloprid Plant Hole Treatment (PHT) was the most persistent to aphids followed by acephate. Imidacloprid PHT (40 g a..i./ ha) and acephate foliar spray (0.075%) required more than 25 days to lose their effectiveness completely. The toxicity of oxydemeton methyl was lost completely in 11-12 days.