This time of the year life is pretty nice if you are a beef cow, pastures are lush, the temperatures haven’t been too hot, and there is very little insect pressure. That will soon change as we move in to summer and the flies will be getting numerous. The following information on fly control is adapted from information from Justin Rhinehart, University of Tennessee Extension Beef Specialist.

The economic loss due to fly infestation in cattle herds has been well studied and documented. Depending on the type of fly and class of cattle, reported economic losses vary but the consensus is that the problem can result in millions of dollars lost to decreased weight gain and health treatments.

There are three major ways that flies reduce performance: through reduced grazing (because cattle are searching for a way to ease the irritation), as a result of sucking blood from the cattle, and through spreading disease. There are a number of flies that can make life miserable for cattle and cost farmers money, they include horn and face flies, deer and horse flies, stable flies, heel flies, and house flies.

Horn and face flies are the two major flies that cause problems for Wisconsin beef cattle producers. Horn flies are small, about half the size of a housefly, and usually concentrate on the withers, back, sides and the underline (where most of the biting occurs). Reduced weight gain from horn flies is caused by irritation (and the resulting decreased grazing time) and blood loss. Normal populations of horn flies usually average several hundred, but as few as 50 flies per animal can be enough to negatively impact performance. Thousands can occur and that many can consume enough of the cattle’s blood to make it become anemic. While most of the discussion around horn flies focuses on irritation and blood consumption, they can also transmit causes of blood-borne diseases like anaplasmosis.

Face flies more closely resemble houseflies. They concentrate around the eyes, nose and mouth where they feed on the mucosa found in those areas. Since face flies congregate around the eyes and can carry the causative agent of pinkeye, controlling them can help slow or limit the spread of pinkeye. The spread of pinkeye by face flies makes their economic impact two-fold. The disease reduces average daily gain in calves and performance of cows but also reduces the value per pound of calves at marketing due to eye problems.

Several methods, and many products within those methods, are available to control flies. These methods include slow-release ear tags, sprays, pour-ons, rubs, dusts, feedthrough and boluses. The most common methods in Wisconsin seem to be ear tags, sprays, pour-ons and rubs. The chemicals that these methods deliver include pyrethroids, organophosphates (OPs), organochlorines and endectocides.

Walk through fly traps have also proven helpful for reducing horn fly numbers on cattle. Plans on how to build a walk through trap can be found at the following website; http://extension.missouri.edu/publications/DisplayPub.aspx?P=G1195

Consider these factors when choosing a fly control program:

Young cattle require more attention than cows and bulls because prevention has a direct economic affect through average daily gain. They also are more susceptible to pinkeye.
Fly tags are convenient but should be used in combination with other methods to achieve full-season protection. Use sprays or rubs early in the season and ear tags as late as economically reasonable.
Self-applicators (face rubs and mops) can be effective ways to deliver concentrated doses of insecticide. These methods should be located in an area where the cattle come in frequent contact with them.
Horn flies quickly develop resistance to first generation pyrethroids. – New formulations are slower to build resistance. – Alternating with OPs can mitigate resistance.
For additional information on fly control, contact your veterinarian, or local extension agent.