Persistence of some newer insecticides in mineral soils measured by bioassay.

Abstract

Persistence of Birlane® (2-chloro-l-(2,4-dichlorophenyl) vinyldiethyl phosphate), Dasanit® ( O, O -diethyl O -[ p -methylsultinyl) phenyl] phosphorothioate, diazinon, Dyfonate® ( O -ethyl S -phcnyl ethylphosphonodithioate), carbofuran, phorate, and Zinophos® ( O, O -diethyl O -2-pyrazinyl phosphorothioate) banded ¾-in. deep in ridges in acidic mineral soils in the laboratory and in Small pots in the field was measured by use of 1st-instar larvae of the cabbage maggot, Hylemya brassicae (Bouche). The materials were most active biologically 3 to 5 days after application in the soil, although Dyfonate, phorate, and diazinon in field tests appeared to be highly toxic to the larvae within 1 to 2 days. Zinophos and phorate degraded in larval toxicity at a constant rate after about 5 days and showed more than 95% loss of toxicity after about 100 days. Diazion became steadily less toxic for about 30 days and thereafter showed only slight further loss in toxicity for the next 2 months. Birlane, Dasanit, Dyfonate, and carbofuran persisted for at least 3 months with little or no loss in toxicity to the larvae but appeared to break down rapidly in late October and November during alternate periods of freezing and thawing of the soil. Carbofuran was the most persistent of the compounds tested and also the most toxic to larvae of the cabbage maggot.