TOXICITY OF CARBAMATE AND ORGANOPHOSPHORUS INSECTICIDE RESIDUES ABSORBED BY RUTABAGAS GROWN IN TREATED SOIL

Abstract

AbstractThe toxicity of residues of three carbamate and nine organophosphorus insecticides in rutabaga, measured by bioassay with larvae of Hylemya brassicae (Bouché), for periods from 60 days after drilling (when roots were 5 to 6 cm diam.) until 150 days after harvest (roots in storage at 4 °C) are presented graphically. The insecticides were applied 3 to 4 cm below the soil surface in a 10 cm band at several rates ranging from 2.8 to 33.6 kg a.i./ha. Maximum toxicity for carbofuran and fensulfothion residues occurred within 75 days of drilling followed by a steady decline. Conversely, the toxicity of residues of trichloronat and chlorpyrifos increased steadily over the growing period with little or no decline during storage. The remaining insecticides exhibited toxicity patterns between these extremes. At high rates, phytotoxicity was recorded for all compounds except trichloronat and fonofos. Phytotoxicity was so severe with AC64475 ((2-diethoxyphosphinylimino)-1,3-dithietane) that all plants were destroyed with rates in excess of 11.2 kg a.i./acre. AC64475 was the most toxic insecticide to H. brassicae larvae. The nine organophosphorus insecticides included in these tests were mostly concentrated in the peel of rutabaga, whereas the carbamates were mostly concentrated in the pulp.