Controlling Flies on Cattle

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With warmer weather, fly populations increase. Horn flies and face flies are the primary pests of cattle here in Burke County. These species breed in fresh manure but each presents a very different management problem. Fortunately, we have a wide variety of fly control options.

Horn flies feed on blood. They remain on animals most of the time; taking frequent small blood meals per day. Populations of just 100 flies along the sides and backs of an animal every day during the fly season can mean 12 to 15 pounds lower weaning weights for spring calves and result in minimal gains for older animals. But because of the close association between the horn fly and the animal there are many effective control options.

horn flies on a black cow

Horn Flies

Photo:  Dave Boxler – UNL Beef

In contrast, face flies spend about 90 percent of their time resting off of animals and return only to feed on liquids around the eyes and face. This renders some fly control methods useless as face flies visit hard-to-treat areas for very short time periods.

Cow with flies on face

Face Flies

Photo:  NC State Extension Entomology

One very effective control method is insecticidal ear tags, which release small amounts of an insecticide distributed over the animal during grooming or rubbing. Typically, ear tags provide excellent, long-term control of horn flies and some brands also reduce face fly numbers. This keeps labor to a minimum, as animals only have to be handled once.

black cow with ear tag

Insecticidal Ear Tag

It is important to read the label before you purchase and use fly tags. Knowing the active ingredient is important and producers should rotate between organophosphate tags and synthetic pyrethroid tags from year to year. This reduces the chances of developing resistance to the active ingredients that are being used.

For effective control, it is best to tag animals after horn fly numbers reach 50 or more per side. Most tags provide 12 to 15 weeks of fly control, so tagging animals too early in the season can mean the tags are not providing control in the fall, which helps keep down the overwintering population.

Another method at our disposal is pour-on products. These are formulations that are applied to animals in measured doses based upon body weight. Horn flies are killed as they land on treated areas of the animal and pick up the insecticide through their body.

Most pour-on products provide about four weeks of fly control, which means they must be reapplied in a timely manner or used in conjunction with other fly control methods. The length of control will affected by weather and other environmental factors, so treat again when fly numbers build back up to about 100 per side, but observe label instruction on reapplications. Many cattle producers like to use dust bags, back rubbers, or automatic sprayers for pasture fly control. They can be purchased ready-made or assembled from easily found materials. These devices are capable of effective horn fly control and done right, can provide excellent face fly control. All require regular maintenance to insure they are working and dispensing properly. Because self-application devices such as backrubbers and bags are not mobile, location is critical for these devices. They must be placed where animals can and will use them regularly. Producers should be sure to provide enough opportunity for treatment as the number needed varies with herd size, pasture size and other factors. The ultimate goal is to get each animal treated regularly.

Finally, producers have the option of using feed through formulations for control. Horn flies and face flies both breed in manure in the pasture and this manure can be treated by having animals consume an insecticide that passes out in the manure. Mineral blocks or loose mineral mixtures are available which contain fly control products. These products are generally some type of growth regulator that affects a certain part of the fly life cycle. This method is intended to be only a part of a total pasture fly control program because horn flies and face flies will migrate from nearby herds. Supplemental control though the use of dust bags or backrubbers will be needed to deal with these migrations.

Beef cattle producers have many alternatives for pasture fly control including ear tags, pour-ons, self-applicators, such as backrubbers and dust bags, along with feed through growth regulators. Cost, effectiveness, past control history and herd management practices should help producers to narrow down their options and minimize the lost production these nagging pests can cause.