Pest Control · October 2025 · 5 min read
Flies reduce livestock performance through irritation, blood loss, and disease transmission. Horn flies alone can reduce calf weaning weights by 15–50 pounds when left uncontrolled. An integrated fly control program that combines multiple methods and rotates chemical classes is the most effective and sustainable approach.
The major fly pests of cattle include:
Count horn flies by observing cattle from 15–20 feet and estimating flies on one side of the animal.
Insecticide ear tags provide season-long horn fly control. Apply tags in late spring when fly numbers reach threshold. Rotate between pyrethroid and organophosphate tags annually to delay resistance. Remove tags in fall to prevent low-level exposure that accelerates resistance development.
Pour-on insecticides provide 2–4 weeks of control and are useful for short-term relief. Dust bags and oilers placed in forced-use locations like mineral stations and water lanes provide continuous self-application by cattle.
Feed-through insect growth regulators (IGR) like methoprene and diflubenzuron pass through the animal and prevent fly larvae from developing in manure pats. Begin feeding IGR 30 days before fly season starts for full effectiveness. This method works best when neighboring herds also participate, as horn flies travel between herds.
Fly parasites (parasitic wasps) are tiny beneficial insects released near cattle congregation areas that parasitize fly pupae in manure. They provide supplemental control and work well as part of an integrated program.
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