STUDIES OF THE DISAPPEARANCE OF 9 PESTICIDES ON CELERY AND LETTUCE GROWN ON MUCK SOILS IN ONTARIO, 1977-1980

Nine experiments involving 7 insecticides and 2 fungicides were conducted with celery and lettuce between 1977 and 1980 to confirm or up-date the current recommendations for registered compounds and to study 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 > 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 5 applications than when 1 or 3 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 > 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 3-14 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 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.