Bioassays on the activation and deactivation of some new insecticides in a mineral soil and absorption of toxic components by rutabagas.

Abstract

Bioassays with 1st larval stages of the cabbage maggot, Hylemya brassicae, (Bouché), demonstrated that subsurface soil applications of phorate and thionazin were highly toxic soon after application but decreased in toxicity during the growing season. Carbofuran became biologically active soon after application and was the most toxic of the compounds tested. Also, toxic components persisted longer than those of thionazin (Zinophos®) (O, O-diethyl 0-2-pyrazinyl phosphorothioate) or phorate at a given rate of toxicant per acre. Chlorfevinphos (Compound 4072) (2-chloro-1-(2,4-dichlorophenyl) vinyl diethyl phosphate), fonofos (Dyfonate) (O-ethyl S-phenyl ethyphosphonodithioate), and trichloronat (Agritox®) (O-ethyl 0-2,4,5-trichlorophenyl ethylphosphonothioate) were the most slowly activated and the most persistent of the compounds tested. Fonofos and trichloronat showed no signs of phytoxicity even at exceedingly high rates, whereas all the other compounds, as well as Dasanit® (fensulfothion) (O, O-diethyl O[p- (methylsulfinyl) phenyl]phosphorothioate) and diazinon, were toxic to rutabagas at rates above 20 Ib toxicant/acre. Carbofuran was the only compound that showed readily detectable upward movement in the soil, and toxicants of this material killed flies resting on the soil surface. Absorption of toxic components of the insecticides by rutabagas grown in treated soil was highest for Dasanit, used as a test standard, followed in order by trichloronat, chlorfenvinphos, fonofos, carbofuran, thioazin, and phorate. Toxic residues of phorate and thionazin were detected in the roots only at high rates per acre, and the toxicants of these materials and of car bofman and Dasanit decreased after 80-90 days. Also, toxic components decreased rapidly in roots in storage. Toxic metabolites of fonofos and chlorfenvinphos decreased slowly in storage and were hardly detectable after 3-4 months. There was no decrease in toxic residues of trichloronat in stored rutabagas for at least 4 months.