Horn Fly Control by the Pour-on Technique Using Ruelene or Toxaphene1

Abstract

Hereford yearling cattle naturally infested with horn flies ( Haematobia irritans (L.)) were treated by the pour-on technique or full-coverage sprays. Treatment was applied to 13 to 14 animals in each of six balanced, adjacent pastures. The animals in three pastures received one treatment, and those in the other three pastures received the alternate treatment. Pour-on treatments consisted of application of 100 ml. of concentrated emulsion applied to the back in each instance by means of a dipper. Comparisons were made of Ruelene® ( O -4- tert -butyl-2-chlorophenyl O -methyl methylphosphoramidate) as pour-on at 9.6 g./animal and US 0.25% spray, and of toxaphene as pour-on at 18 g./animal and as 0.5% spray. The pour-on procedure provided superior control in terms of absolute reduction of fly numbers and of length of time treatment remained effective. The toxaphene treatments were notably more effective than the Ruelene treatments by both application procedures. Erythrocyte cholinesterase levels were mildly depressed and were significantly lower among the Ruelene-pour-on animals than among the Ruelene-sprayed animals (82% vs. 88% of initial activity). No skin irritation was observed in any instance.