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Managing Flies in the Summertime

University of Minnesota Extension, Stearns County News
August 3, 2016        
Source:  Emily Wilmes, Extension Educator-Livestock
University of Minnesota Extension
Stearns, Benton & Morrison Counties

Managing Flies in the Summertime
By Emily Wilmes, University of Minnesota Extension

ST. CLOUD, Minn. (08/03/2016) — In the summer, it always seems like if it’s not one thing it’s another.  If it’s not the heat, it’s the flies.  As much as flies and insects may bother us during the summer, just imagine the additional stress they put on cows.  Not to mention that they can also be a threat to the cow’s health.  Mastitis-causing bacteria on biting flies can be spread among cows when flies congregate on teat ends. Research has shown that heifers and cows in herds with fly control programs have lower prevalence of mastitis than in herds without fly control.  Because of these threats to herd health, it’s crucial to practice some form of fly control on your farm.

Fly control consists of three main types: chemical, biological, and physical.  Chemical control methods exist for different life stages. Make certain any pesticide selected is approved for use in lactating dairy animals. For maximum effectiveness, use chemicals that abort the larval stage as well as chemicals that kill adults. Chemical-impregnated ear tags and fly blocks are a popular fly control method for cattle. Other chemical control methods include foggers, exit lane dusters, and pasture back rubs.

Biological fly control uses natural enemies of flies to reduce fly populations.  Many bird species feed on flies, including bluebirds, purple martins, and tree or barn swallows. Each of these birds will capture and eat hundreds of flies daily. Parasitic wasp larvae are another biological control method. These wasps will invade a host when they are in the larval stage, and kill the insect by acting as a parasite.  These larvae may be purchased from biological supply houses. These wasps are a safe option as the small adult wasps do not sting cattle or humans.

A physical form of fly control is an electric pass-through station. These are another effective control method. The cattle pass through a short tunnel. Black lights encourage the flies to leave the animal and pass through electric-charged panels where the flies are electrocuted.  Of course one of the most effective and cheapest ways to keep flies away from your cows is to keep their environment clean.  Strict sanitation and mortality management, especially around calving areas, silos, grain bins, and hay racks, plus prompt manure removal and disbursement help control these pests.

If you have any questions about fly control on your farm, visit


Emily Wilmes
Extension Educator, Ag Production Systems - Livestock
(320) 255-6169
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