Whether in the pasture or the barn, fly control is an essential part of keeping healthy dairy and beef cattle herds, said Purdue entomologist Ralph Williams.
In pasture cattle the two primary fly pests are horn flies, which are a biting fly, and face flies. Face flies do not bite, but they feed around the eye tissue and can transmit bacterial conjunctivitis, or pink eye.
"Horn flies are the number one fly pest in the United States," Williams said. "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 do not transmit disease, they can cause economic loss by reducing 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. There’s no disease associated with them, but they, too, can result in economic loss.
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 said. "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. Insecticides can be effective as long as they stay on the animal for an extended time. One such method is through pesticide ear tags.
"For flies in the pasture, insecticide ear tags are really the most suitable to control both face flies and horn flies," Williams said. "Some of the products available are pyrethroids and organophosphates. 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 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, also can disrupt flies. But, if not all cattle in the area are using them, flies could still be present.