Fly Control Using Ear Tags

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Insecticide-impregnated ear tags or “Fly Tags” are a convenient way to control pasture flies (especially horn fly). Tags are inserted in late spring, or early summer, and your fly control program travels with the animal. However, continued use of tags with the same insecticide for several consecutive seasons can lead to populations of the horn fly that have resistance to a whole class of related insecticides. This will cause a shorter than normal period of fly control, and testing would be needed to confirm resistance.

To further complicate the issue, there are several other things that could cause reduced fly control. Fly Tags have a limited duration of effectiveness. The 12- to 15-week “fly control clock” starts when tags are inserted. Applying them too early in the spring can mean control “runs out” before fly season is over. In addition, Horn flies can move in from untreated nearby herds and keep populations high, making control seem less effective. As well, above average precipitation can keep manure pats moist longer, making them more suitable for horn fly breeding as opposed to hot, dry summers when they dry quicker and are less hospitable for horn fly maggots.

There are several ways producers can get the most out of their ear tag-based fly control program. First, rotate insecticide classes annually. Currently there are three options—organophosphates, pyrethroids, and chlorinated hydrocarbons—but dozens of brand names. Check the label for the name of the active ingredient in the tag to be sure you know what you are using and record the choice each year. Next, always apply tags after horn fly numbers reach about 100 per side per animal. This will prevent applying them too early. It takes more than 100 flies per side to have an impact on weight gain. Lastly, supplement fly tags with dust bags, oilers, sprays or pour-ons, if needed.

Staying on a pro-active program will keep resistance problems at bay, and you will help keep your cattle more comfortable, healthy, and productive during the active fly season.