Aharonson, N., Pesticide Chemistry and Residue Research Laboratory, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel
Ben-Asiz, A., Pesticide Chemistry and Residue Research Laboratory, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel

The persistence of Velsicol VCS-506 [O-(4-bromo-2,5-dichlorophenyl)-O-methyl phenylphos-phonothioate] insecticide, its O-analog, and phenol derivative (2,5-dichloro-4-bromophenol) was studied on tomatoes and grapes grown in the coastal plain of Israel during the summer and fall. Chemical analysis of tomato plants sprayed with VCS-506, 3500 g of emulsifiable concentrate/ha, showed that the residue level in the fruit was the same 1 and 21 days posttreatment. During the same time interval, there was only a 20% reduction in the residue level of Velsicol VCS-506 in the leaves, whereas between the third and fifth weeks after treatment, the rate of degradation increased. In grapes that were dipped in a 2.5% VCS-506 emulsifiable concentrate emulsion the residue level was 12 ppm 1 day after treatment and 7.5 ppm 44 days later. The concentration of the phenol derivative in all the samples was 1-10% of that of the parent compound. In both tomatoes and grapes, the highest concentration of this derivative was found 3 weeks after treatment. Accumulation of the O-analog was not found. Translocation of the parent compound from leaves to fruit was not observed, but some translocation of the phenol derivative was detected. Results from the chemical analysis were confirmed by the tic enzymic inhibition technique. Additional cholinesterase-inhibiting metabolites were not detected. Field application was according to the recommended amounts and procedures.