The piercing, sucking mouthparts of adult horn flies are barely visible to the cattle producer’s eyes, but the havoc they inflict each year on his or her cows—and pocketbook—is painfully bruising.

“The horn fly is a chronic, ubiquitous pest that costs producers more than $1 billion annually,” says Nancy Hinkle, a University of Georgia professor of veterinary entomology who has studied the fly for more than 30 years.

Closer to home, the horn fly quickly paints an ugly picture in your own pastures as scientific studies reveal:

  • Calf weaning weights can drop by up to 20 lb. when horn flies aren’t adequately controlled in a herd of mother cows.
  • Yearling weights can plummet up to 50 lb. when the pests are given free rein to populate pastures and suck on blood.

“Horn flies don’t coordinate dining efforts, so when there are 100 or 200 flies on the backs and undersides of cattle, there is probably at least one fly feeding every single minute of the day,” Hinkle says.

And, she emphasizes, “Since those flies torment cattle so badly, the cows spend their time swinging heads, twitching tails and kicking bellies instead of feeding. All this activity increases body temperatures and energy expenditures, which are not conducive to weight gain.”

Calves become unfortunate victims, too. Their feeding is interrupted as mothers try to ward off biting flies. And the amount of milk produced can drop sharply because the flies are vectors of summer mastitis.

Both Hinkle and Larry Hawkins, a technical services veterinarian at Bayer Animal Health, say that the far-reaching damage can be reduced substantially if producers carry out a well-designed and executed integrated pest management plan using insecticide ear tags in combination with pour-ons, dust bags, back rubbers, sprays and oral larvicides.

“Depending on the year, you will get 12 to 15 lb. of added gain on the calf if you control horn flies on the cow,” Hawkins says. “In some years, it will be significantly more than that, but rarely will it be below 12.”

But Hawkins and Hinkle agree that the success hinges heavily on rotating between active ingredients and modes of action because insecticide resistance has become a major problem with horn fly control.

“I hope that pesticide companies continue to develop new products because cattle producers are in a constant race with these flies,” Hinkle says.

Hinkle and a team of researchers have analyzed one new product on the market—an ear tag that utilizes the active ingredient tolfenpyrad.

“We tested it during the 2015 horn fly season and were quite impressed with the results,” she notes. “We got very good horn fly control through the duration of the study.”

The research shows that Tolfenpro™ tags can effectively be worked into a successful rotation program, says Hinkle, who then puts emphasis on the word rotation.

“If 100% of the horn fly population is being exposed to the same insecticide continually, resistance is inevitable,” she says. “That’s why it’s important to have a sound rotation plan, and, if possible, please work with your neighbors.”

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