Insecticides are usually ineffective since the insects spend little time on the animals. Insecticide treatment of breeding areas is also impractical. Several factors have been suggested to explain the difficulties of controlling horse flies in field situations where it is not feasible to handle the animals on a frequent schedule. Some degree of repellency can be obtained for two or three days after applying a spray mixture of pyrethrins and piperonyl butoxide. Use of this mixture may benefit dairymen or small herd owners in areas of heavy local infestation.
Insecticides currently registered on cattle only afford moderate control of horse flies at best.
Spray the entire body of the animal, paying particular attention to the areas most frequented by the horse flies. Frequent treatment may be necessary. Your county Extension agent has information concerning which insecticides to use. Glenn Studebaker , Extension Entomologist, is located at the Northeast Research and Extension Center, Keiser. Dr. John D. Hopkins is an Assistant Specialist - Entomology and Insecticide Testing Coordinator, Cooperative Extension Service, University of Arkansas, Lonoke Agricultural Center, Lonoke.