Flies can transmit diseases and reduce weight gain and feed efficiency in cattle.
They buzz and they bite, but the flies that cause a nuisance to people can also bring disease and nuisance to cattle. Fly control is essential in maintaining the health of dairy and beef cattle herds, whether in the pasture or the barn, says Purdue University entomologist Ralph Williams.
For pasture cattle, the two primary fly pests are horn flies, which are a biting fly, and face flies. Face flies don’t bite, but they feed around the eye tissue and can transmit bacterial conjunctivitis, or pink eye, to cattle.
"Horn flies are the No. 1 fly pest in the United States," Williams says. "The threshold at which we recommend control is when those flies reach 200 per animal. It is not uncommon to see a thousand or more horn flies per animal."
While horn flies don’t transmit diseases to cattle, they can cause economic loss by reducing cattle weight gain, feed efficiency and calf weights.
For cattle in confinement, the stable fly is a biting fly that breeds in the accumulating feed waste and soiled bedding. As with the horn fly, stable flies don’t carry disease, but they, too, can result in economic loss for farmers.
House flies are the other common confinement pest. While they're not directly associated with cattle, they can be a nuisance to people and surrounding neighbors.
"In confinement flies are best controlled through sanitation," Williams says. "Farmers should identify and remove fly breeding sites, like waste and soiled bedding."
In the pasture, however, fly control can be a bit more challenging. Topical insecticides can be effective as long as they stay on cattle for an extended time. One such method is through pesticide ear tags.
"Some of the products available are pyrethroids and organophosphates,” Williams says. “The pyrethroid-based tags generally are not very effective for horn flies because of a genetic resistance. Most of the organophosphate tags are very efficient for horn fly control. Abamectin is a new product that is available in some tags and has been very effective for both horn flies and face flies."
Some tags also are available with a combination of insecticides that will control both face and horn flies.
Other fly-control options include self-applied dust bags in a forced-use situation, which cattle need to access daily, and pour-on insecticides, which can last up to a month. Feed-through insecticides, ingested with feed and released in the manure, can also disrupt flies. However, if not all cattle in the area are using them, flies could still be present.
As a biological fly-control option, farmers can introduce parasitic wasps to the farm. The females of these wasps lay eggs on fly pupae, and the wasp larva consume the fly before it emerges. Parasitic wasps may be purchased by biological pest control companies, which provide beneficial predator insects.