For most of cattle country, winter is a bygone memory. While drought still plagues cattle producers, particularly in the Far West, rains have blessed many pastures and spring and summer grazing is upon us.

That means so are the winged annoyances that bother cattle and hurt productivity. According to David Boxler, Extension educator-livestock entomology at the University of Nebraska-Lincoln in North Platte, Neb., there are two fly species of importance to cattle producers—the face fly and the horn fly.

Face flies are pasture flies that feed on secretions, such as eye irritations or other things that cause an animal’s immune system to exude a secretion onto the skin. Adult female face flies often cluster around an animal’s eyes, mouth and muzzle, causing extreme annoyance, Boxler says.

“Face flies ae economically important to cattle producers, since they can transmit several eye diseases and parasites to cattle,” Boxler says. These diseases include pinkeye and infectious bovine rhinotracheitis (IBR), and the flies can be a source of a nematode eye worm.

However, it’s the horn fly that really gets a cattle producer’s goat—and his cattle as well. “The horn fly is considered one of the most important blood-sucking pests of pastured cattle and can have significant economic impact on animal performance,” Boxler says.

Horn flies remain on cattle most of the time, and feed on the animal’s blood. During the heat of the day, they often congregate on the animal’s belly, seeking shade.

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Economic losses associated with horn flies are estimated at more than $800 million annually in the United States. Horn flies can cause blood loss, reduced grazing efficiency, reduced weight gain and a drop in milk production. While horn flies are inclined to infest larger animals, such as bulls and adult cow, they will attack calves as well, Boxler says.

“Nebraska studies demonstrated calf weaning weights were 10-20 pounds higher when horn flies were controlled on cows,” Boxler says. “Other studies utilizing stocker cattle and replacement heifers demonstrated that treated animals had an 18% weight gain advantage over untreated animals.”

Treatment options

Here’s a list of treatment options to consider as the fly wars heat up:

Insecticide ear tags are one of the best devices for deterring flies. If you use insecticide ear tags, Boxler suggests these management tips:

    2. Waste management

Remove the places where flies breed, and you will start to notice a significant decrease in the number of flying foes circling your herd. “Buildup of organic matter is the biggest breeding grounds for flies,” says Mike Peacock, Southern States Cooperative ruminant nutritionist. With the average 1,250-pound beef cow generating 75 pounds of manure a day, this leaves many areas for flies to reproduce.

On average, the fly life cycle lasts anywhere from 10 to 21 days. To break the fly cycle, you need to remove fly-breeding material on a regular basis. Manure, wet grain, spilled silage, moist hay — focus on these areas first.

“You can eliminate a large portion of flies by simply cleaning the hay rings where cattle were fed all winter,” Peacock says.

To further eliminate breeding areas, start by removing manure from livestock pens as frequently as possible. Take the manure and spread it thinly on fields or other large outdoor areas to facilitate drying. Flies cannot develop in dry environments, therefore they cannot develop in dry manure. Drag your fields to more evenly distribute manure. The key is to dry out the manure.

Remember, it’s easier and more cost-effective to prevent fly breeding than to try and control adult flies already born. The quicker you can remove their habitat and breeding grounds, the better off you’ll be.

Dust bags can be a low-maintenance and effective way to combat flies. “This fly control technique requires fencing around a water tank or mineral feeder and suspending dust bags at the entrance-exit gate,” Boxler says. “Dust bags placed in a forced-use situation will usually reduce fly numbers by 80-90% throughout the season if properly maintained. Dust bags in a free-choice design (like a loafing area) will provide 25-50% less control than a forced-use dust bag design,” he says.

Back rubbers are used much in the same way as a dust bag. A small amount of oil or insecticide gets on the animal as it rubs under the device. “When charging a back rubber, use a quality grade mineral oil or fuel oil (not motor oil) to mix with the insecticide to avoid irritation,” Boxler says. Back rubbers and oilers are most effective when used in a forced-use design, he adds.

Pour-ons are ready-to-use formulations poured along the backline of cattle. “As a rule, they provide several weeks of fly reduction, so they must be re-applied throughout the fly season,” Boxler says.

Animal sprays can be effective in controlling horn fly populations, Boxler says, but it’s important to get complete coverage of the animals. High pressure sprays may provide better coverage, but it’s necessary to gather and corral the cattle, which may make this application method unpractical.

Sprays can also be delivered using a mist blower or low pressure sprayer mounted on an ATV. With this method, you can drive to where the cattle are and apply the insecticide by driving around and amongst the cattle.

Oral larvicides, such as feed additives and boluses, are products that are incorporated into minerals or other feed products. The insecticide passes through the animal’s digestive tract into the manure, where it prevents fly larvae from developing into adults. “To be effective, cattle must consume a label-specified amount on a daily basis,” Boxler says.

Not all flies are bad. Fly predators, nature’s own self-inflicted enemy, can be your ally in the fight against pest flies. These are tiny, non-stinging, non-biting wasps that feed on fly larvae and interrupt the breeding cycle of flies, destroying the next generation of flies before they hatch into disease-carrying adults, Peacock says.

Fly predators work by both laying eggs in the fly pupa (or cocoon) and feeding on fly larvae while it’s in the manure on your farm. The wasps “bug” the bugs but never disturb the cattle, pasture plants, or humans for that matter.

Although a natural method of controlling flies, fly predators aren’t typically found in large enough amounts to control the entire fly population on your farm. However, many companies sell fly predators and can ship them straight to your farm. Once they arrive, all you have to do is sprinkle the predators on manure piles at dusk and watch them go to work.

As a rule of thumb, replenish your fly predator supply once a month from April to September. It’s important to use them during the entire fly season; otherwise the fly life cycle will only be broken for a few weeks.

Don’t get frustrated if you don’t see an immediate reduction in fly populations. Both face flies and horn flies can travel several miles in search of cattle. If you’re managing your fly population, but your neighbor isn’t, you may be getting “flies without borders” as they travel in search of a meal. With an ongoing fly management program, however, both you and your cattle should rest a little easier.

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