Flies can bite into a rancher’s profit

Few pests are more annoying to beef producers than flies, and it’s really no wonder.

Flies are scavenger pests. They eat all kinds of undesirable things, like dead animals, plant waste and manures. They play an important role in a functioning ecosystem, but those same attributes make them dreadful for cattle, where the hovering, buzzing and biting cause pain and distress in bovines, reducing their ability to gain weight.

Cassandra Olds, Extension entomologist at Kansas State University, said fly problems seemingly are getting worse, due to selection pressure caused by repeated use of permethrin insecticides to treat them.

“Genetic mutations occur naturally over time, especially in organisms that have very short generation times and large numbers of offspring,” Olds told the audience at Cattle U in Manhattan June 25.

And that, she added, “is why we have insecticides that used to work before, that aren’t working anymore.”

Know the species

All flies are not the same, Olds said. They have different ways to breed; different impact on cattle; and different treatment protocols.

Stable flies are the first fly species we see in the spring. They feed one to two times per day, for three or four minutes per time, on the lower part of the animal – which is why you see cattle standing in ponds, she explained.

“Flies need 20 minutes of contact time to elicit a response to insecticide,” Olds said. “So stable flies are getting micro doses of insecticide, which won’t kill them.”

Stable flies reproduce anywhere there is decaying plant matter, so hay bales, mowed grass and lawnmower clippings are great hosts, she said. A typical round bale can produce 58,000 stable flies per week.

Stable fly bites cause pain and distress to cattle, causing cortisol levels to increase and reduce the time cattle feed. Ten flies per front leg can reduce weaning weights by 38 pounds; in stockers, reducing from just four stable flies to one can increase average daily gain by 0.6 pounds, she added.

Horn flies feed in a “head down” orientation on cattle, and they reside on an animal 24 hours per day, seven days a week.

“Once they pick an animal, that is their animal. That’s why you see some animals have lots of flies, and some have very few flies,” Olds said. 

Horn flies tend to impact milk production, weight gain and horn maintenance, although each animal can withstand 200 to 300 flies before treatment is warranted.

“We always suggest waiting to apply an insecticide until numbers reach those limits,” she said. Producers are advised to put ear tags in stocker calves early, even though the flies aren’t present in the early part of the stocker season. However, ear tags will suppress flies as the flies become active, she added.

Face flies feed on mucus and secretions from nasal passages and eyes. They aren’t a large problem in Kansas, but they can cause pinkeye transmission.

Controlling flies

The most important way producers can control flies is to remove habitat, Olds urged. Clean up trampled hay, even if it is inconvenient.

“Think about all the ways you can reduce the amount of hay wastage. Maybe it is going to cost me an extra trip to the pasture, but think about those 200,000 flies that reproduce and how much that convenience costs,” she said.

Olds added that insecticide use is an important component of fly control.

Producers need to use the correct insecticide for the target fly species.

“In feedlot and confined locations area sprays, residual sprays, larvicides, baits and certain feedthroughs are often used to control house flies and stable flies,” she said. “For pasture fly control, back rubbers/oilers and dust bags are often placed near water tanks or mineral stations where animals will use them on free choice basis.”

Pour-on products are often applied before animals are sent to pasture. Some of the products are absorbed through the skin and work internally, while others work by contact.

Feedthroughs can also be used to manage pasture flies. Animal sprays and insecticide ear tags are also very popular options.

Olds said producers must rotate mode-of-action between pyrethroids, organophosphates and macrocyclic products to prolong the effectiveness of fly insecticides.

“Once you have resistance, it’s not going to go away,” she said.

Bill Spiegel can be reached at [email protected].