Studies of the disappearance of nine pesticides on celery and lettuce grown on muck soils in Ontario, 1977–1980

Nine experiments involving seven insecticides and two fungicides were conducted with celery and lettuce between 1977 and 1980 in order to provide data which would confirm or up-date the current recommendations for registered compounds, and also to provide data on the disappearance rates of alternative non-registered insecticides. Endosulfan, applied to celery at a rate of 0.8 kg ha−1, required 14 days to decline below the tolerance level of 1.0 mg kg−1; residues of methomyl on celery declined below the tolerance level of 2.0 mg kg−1 within the first 3 days. Parathion, when applied as an emulsifiable concentrate to celery, required greater than 21 days to decline to the tolerance level of 0.7 mg kg−1, compared with 10 days when applied as a wettable powder. Applications of parathion on celery, at repeated weekly intervals at a rate of 0.3 kg ha−1, produced significantly higher initial residues with five applications than when one or three applications were made; after 10 days from the terminal application, there were only slight differences in residue levels. Maneb and zineb residues declined below tolerance levels within 3–7 days following application. Alternative insecticides investigated for use on celery and lettuce included acephate, cypermethrin, fenvalerate and permethrin. Celery, treated with acephate at a rate of 0.75 kg ha−1, required more than 13 days for residues to decline below a negligible level (0.1 mg kg−1); the disappearance of acephate in lettuce appeared to be somewhat faster, requiring from 3 to 14 days to decline to the 0.1 mg kg−1 level. Cypermethrin, fenvalerate and permethrin, all applied at the rate of 0.08 kg ha−1, disappeared rapidly on both celery and lettuce, and the residues fell below 0.1 mg kg−1 within 8–14 days on celery, and within 3–7 days on lettuce.