K-State Research and Extension Johnson County

Flies on Cattle

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Horn flies are considered the most important external parasite of cattle. High summertime populations cause cattle to lose weight and lower milk production. Keep these points in mind when considering fly control:

  • Begin horn fly control procedures in the spring when cattle average approximately 200 horn flies.
  • If ear tags are used, the insecticide classes must be rotated. Do not use a pyrethroid ear tag more than once every three years. Do not use an organophosphate ear tag more than two years in succession. Continuous use of ear tags in the same insecticide class will eventually result in horn fly resistance.
  • Remove ear tags at the end of the fly season or when they lose their effectiveness. Do not tag cattle more than once per fly season, regardless of insecticide class.
  • If additional horn fly control is needed later in the year, use sprays, pour-ons, dusts or back rubbers. If possible, alternate insecticide classes when changing control methods.
  • Use ear tags on heifers, cows and weaned calves. Not on bulls and calves still on their mother.

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