Department of Entomology, Haryana Agricultural University, Hissar
Residus analysis of carbaryl and tetrachlorvinphos on tomato by bioassy using Drosophila melanogaster Meign. as the test insect, was made. Tomato crop in fruiting stage, was sprayed with carbaryl and tetrachlorvinphos @ 1 and 2 kg a. i./ha. Fruit samples were collected at 0, 1, 3, 7, 10, 15 and 21 days after spraying and analysed. Carbaryl was found to be more persistent than tetrachlorvinphos. Though both doses of the insecticides resulted in corresponding deposits, the rates of dissipation were more or less the same. Dissipation was faster in the beginning but became slow later on. The residue of carbaryl declined to safe limits of 10 ppm within 10 days of spraying while tetrachlorvinphos took seven days to come down to this limit.
Washing of 2 kg a, i./ha treated fruits, for one minute, under tap water, removed 75 and 79 per cent of the initial deposits of carbaryl and tetrachlorvinphos, respectively. In order to avoid hazards from residues, tomatoes treated with carbaryl may be harvested after 10 days of spraying and those with tetrachlorvinphos after a week.
