Residues and persistence of some organophosphorus insecticides applied to cabbage plants

Cabbage plants grown in a field experiment were sprayed with E. C. formulations of malathion, pirimiphos-methyl and prothiofos at the rates of 570, 600 and 750 g a.i. per feddan; residues of the three insecticides were analysed by GLC. Results revealed that initial deposits varied; the highest deposit was that of malathion followed by pirimiphos-methyl, and the lowest initial deposit was that of prothiofos. Initial deposits on inner leaves were less than the outer leaves. Prothiofos showed more persistence than malathion, the least persistent toxicant was pirimiphos-methyl. Persistence of the toxicants was lower on inner leaves, probably owing to lower initial deposits. Deposits were within the permissible limits after 12, 12 and 15 days for malathion, pirimiphos-methyl and prothiofos, respectively, while on inner leaves, these intervals were 6, 8 and 12 days for the same insecticides, respectively.