September 2, 2014

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Fly Control Using Ear Tags

Lindie Huffman, Agriculture and Natural Resources

Insecticide-impregnated ear tags are a popular means to control pasture flies (especially horn fly). Tags are inserted in late spring or early summer, and the fly control program travels with the animal. However, using tags containing the same class of active ingredient for several consecutive seasons can select for populations of the horn fly that are resistant to a whole class of related insecticides. This shows up in the form of a shorter than normal period of fly control, but lab testing would be needed to confirm resistance.
To cloud the issue more, other things could cause reduced fly control. Some examples:

The 12- to 15-week "fly control clock" starts when tags are inserted. Hanging them too early in the spring can mean protection "runs out" before fly season is over.

Horn flies moving in from untreated nearby herds can keep pressure high and make control seem less effective.