DDT and dieldrin residues on pasture following dusting and spraying

Abstract

Abstract DDT was applied to short, dry pasture as an emulsion spray, dry mix/DDT superphosphate dust, or “wet” mix DDT/superphosphate dust, at the nominal rate of 2 lb pp'-DDTlac. Similar pasture was treated with dieldrin at the rate of 4 oz/ac as an emulsion spray or as a dieldrin/superphosphate dust. Residual insecticides were determined on the pasture at intervals up to 42 days. Pasture contamination with DDT was highest from spraying, residues being approximately 10 times greater than from the DDT/superphosphate dusts. There was essentially no difference in DDT residues from dry and “wet” mix DDT/superphosphate dusts at equivalent rates of application. Initially residues resulting from dieldrin spraying were higher by 60 per cent than from dieldrin/superphosphate dusting but both treatments gave similar dieldrin residues 28 and 42 days after application. It was concluded that while rainfall and plant movement caused mechanical loss of insecticide deposits in the one to two weeks following treatment, subsequent residue reduction was mainly the result of dilution by plant growth.