Photo of a black cow infested with horn flies. — Horn fly infestations can deliver hundreds of painful bites to affected cattle. (Photo courtesy of the OSU Department of Entomology and Plant Pathology)

Small horn flies can be big problem for livestock

Thursday, June 10, 2021

Media Contact: Donald Stotts | Agricultural Communications Services | 405-744-4079 | donald.stotts@okstate.edu

Horn flies cause billions of dollars of damage and economic loss to the cattle industry each year, but for producers, managing these pests is a personal drain on the wallet.

Like a horde of fearsome movie vampires, horn flies are voracious bloodsuckers often found in association with grazing cattle, said Justin Talley, Oklahoma State University Extension entomologist.

“Horn flies are at their highest populations from April through October in Oklahoma,” he said. “In hot weather, horn flies can complete their life cycle from egg to adult in 10 days, resulting in explosive population growth. Emerging horn flies may travel 10 miles searching for cattle but will most likely stay within a couple miles if cattle are around.”

Infested cattle often signal the problem by licking their backs, twitching their skin, switching their tails and tossing their heads.

Studies across the United States have indicated the most effective way to control horn fly populations is to take an integrated pest management approach to both the adults and larvae. Just treating for adult horn flies will not be sufficient, Talley said.

Control of horn flies should begin when 200-300 flies per animal are observed. Researchers have shown that 15-30 pounds of extra gain in calves is achieved over the summer when horn flies are controlled. Ear tags continue to provide a convenient method of horn fly control.

“It’s important to note resistance across the state varies with past usage of ear tags containing pyrethroids,” Talley said. “Producers should rotate their ear tags every year. If additional treatment is needed, then use a program that utilizes sprays, pour-ons, back-rubbers or dust bags.”

Talley recently provided additional insights about horn fly management on the agricultural television show SUNUP.

OSU Extension recommendations are to not use ear tags containing pyrethroids for more than one year. Various studies have shown alternating control procedures will provide the best long-term horn fly control. Additional key elements include:

Horn flies lay their eggs in fresh manure, so use a commercial Insect Growth Regulator (IGR) to help prevent large populations by killing the larvae.
Use a feed-through IGR in a mineral supplement and combine this with an insecticidal ear tag.
Rotate grazing of cattle between pastures to minimize manure accumulation in one area.
Treat bulls with a spray or pour-on application, as this will disseminate product more evenly than an ear tag in the case of bulls.
Consider pyrethroid products that are synergized because the agent known as piperonyl butoxide (PBO) will bypass some of the insecticide resistance mechanisms in horn fly There are more than 2,500 pesticide products that contain the active ingredient PBO.

In addition to the hundreds of painful bites that agitate cattle daily, lesions can lead to secondary infections — and even cosmetic defects in tanned or dyed leather. Horn flies have been found to be a carrier of Stephanofilaria stilesi, a nematode that causes a granular dermatitis that occurs mainly on the belly, scrotum, prepuce and udder of cattle in the western United States.

Horn flies also attack bison, buffalo, horses and other large mammals. Beneficial predators, parasites and natural competitors occur naturally in horn fly breeding locations, Talley said. Predatory mites, beetles, and other fly larvae feast on the developing horn fly larvae.

Fact sheets detailing research-based recommendations for pest control are available online through OSU Extension and through OSU Extension county offices.