Malathion Residues in the Milk of Dairy Cows Treated for Horn Fly Control1

Abstract
A series of trials were conducted to determine the usefulness of malathion for control of the horn fly, Siphona irritans, on dairy cattle. Hand application of 4% malathion dust at a rate of 2 ounces per cow resulted in malathion residues in the milk of not more than 0.01 ppm 12 to 60 hours after treatment. Similar treatment with 10% malathion dust and a 0.5% malathion spray application resulted in significantly greater residues. The 3 formulations of malathion did not appear to differ markedly in their effect on the horn fly. Useful levels of fly control for a period of 9 to 14 days were obtained.

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