Fly control on beef cattle in pasture situations can become an issue during the summer months. The two most commonly talked about fly pests are the horn fly and the face fly, but deer and horse flies can also become a nuisance. I have not seen any kind of economic threshold set for face, horse or deer flies that corresponds to an economic loss, although common sense says that if an animal is running from flies, or spending energy trying to rid itself of flies rather than grazing, then some type of performance loss is occurring. There has been enough research done with horn flies, which spend most of their life on cattle, that an economic threshold has been established. The goal is to keep horn fly numbers below the threshold of 200/animal. Research has demonstrated that horn fly control can result in an additional 12 to 20 lbs. of weight/calf over the summer month, as well as reduced weight loss for the cow.
There are a variety of methods that can be used to control the horn fly, and some that also offer some control of the face fly. The method used may depend upon the cost, convenience, pasture layout and effort the cattle manager wants to put into control. In general, control methods can be defined as chemical, mechanical, biological and genetic. One of the issues with chemical fly control is fly resistance to chemicals. Effective use of chemical control depends upon the cattle manager knowing what chemicals are working and following label directions to minimize and slow down resistance problems.
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