Comparisons of residues in milk resulting from two types of spray applications of DDT, Shell Compound 4072, and ronnel.

Abstract

In tests to compare residues in milk resulting from application of insecticide sprays to dairy cows, the animals were covered completely with a spray of a concentration sufficient to leave a residue for 1 to 4 weeks or with a mist-spray applied by an automatic device. The mist-spray dispersed approximately the minimum required to control horn flies, Haematobia irritans (L.), for 1 day, thus avoiding any heavy deposits on the animal. The insecticides tested were DDT, ronnel, and Shell Compound 4072 (2-chloro-1-(2,4-dichlorophenyl) vinyl diethyl phosphate). Residues of each insecticide present in the milk after the sprays were applied were determined by gasliquid chromatography. Results showed that residues of insecticides in milk can be greatly reduced by proper use. When minimum amounts for horn fly control were applied to dairy cows in small daily doses, residues from all 3 insecticides were extremely low.