With fly season approaching, now is the time to evaluate and refine your fly management plan for 2026.
“Every year, stable and horn flies cause significant economic losses, but a good fly control program can minimize this impact,” says Cassandra Olds, Kansas State University Extension entomologist. “Although often grouped together, these are very different flies that need different control approaches.”
Dr. Ashby Green, Neogen senior technical services veterinarian, says, “If you are seeing flies, ticks, lice or insect damage to your cattle herd, we know there is an economic impact; however, that impact can become far greater than production or weight gain loss alone. Insect pressure affects grazing patterns of cattle; it affects their comfort and it can lead to health issues. Some of those health issues can be definite, such as anaplasmosis.”
The vectors responsible for spreading anaplasmosis include horse flies, stable flies and ticks. This condition has been reported in most states across the U.S., while the disease has been recognized as endemic throughout the South and several Midwestern and Western states.
Jonathan Cammack, Oklahoma State University assistant professor and state extension specialist, says, “With horn flies, we’re looking at mastitis risk, so that’s going to impact both dairy cattle and also our cow-calf operations. A lot of times, horn flies will feed on the udders of the animals, and they transfer the Staphylococcus aureus bacteria because they land on the manure, then they go back to the animal to feed and bring those bacteria with them.”
Several other conditions are propagated by flies, including pinkeye, which can be spread by face flies and causes inflammation and ulceration of the eyes. Pinkeye-affected calves are, on average, 35 lb. to 40 lb. lighter at weaning compared to healthy calves, according to a University of Kentucky report.
Cammack predicts flies are costing the U.S. cattle industry $6 billion annually in losses.
“That encompasses everything from actual loss in production due to decreased weight gain or decreased milk production, veterinary needs associated with treatment of cattle with exposure to pathogens from some of these insects, and then also the control measures associated with managing those individual fly species,” he explains.
David Boxler, Nebraska Extension livestock entomologist, says if previous control efforts underperformed, consider adjusting your approach.
“The best control method will depend on several factors including efficacy, cost, convenience and your current herd management practices,” he summarizes.
He also reminds producers that horn flies can migrate from neighboring untreated herds, masking the effectiveness of your efforts and increasing fly pressure. For this reason, Boxler recommends a comprehensive, integrated fly control.
Olds shares these tips for stopping flies, or at least reducing their impact:
Step 1: Know What You Have
“The first step in developing a good fly control program is knowing who you have,” Olds explains.
Horn flies feed 20 to 30 times a day and stay associated with their chosen animal 24/7, with females only leaving briefly to lay eggs. Stable flies in contrast only feed once or twice a day, remaining on the host for a short period of time (3 to 5 minutes).
When not feeding, flies are resting in shaded areas such as building sides and vegetation. This short feeding time means producers often underestimate their stable fly burdens. While both flies affect pastured cattle, horn flies are not a problem in confined settings such as dairies and feedlots. This is because horn flies need fresh, undisturbed manure as a breeding site while stable flies can develop in any decaying plant matter such as hay bales, feed bunk spill over and decaying grass.
“Their populations can build rapidly and often exceed the economic injury level defined as 200 flies per animal,” Boxler adds about horn flies. “Once fly numbers surpass this threshold, cattle experience reduced weight gain and milk production due to fly-induced stress and altered grazing behavior.”
Step 2: Reduce Populations
Olds explains with either fly species, using non-insecticidal control methods is essential for slowing insecticide resistance. For horn flies, pasture burning in spring kills any flies overwintering, which can significantly reduce fly populations emerging as weather warms. A healthy dung beetle population will also significantly reduce your fly numbers for free.
“Dung beetles are very susceptible to macrocyclic lactones so avoid using injectable and pour-on avermectins (abamectin, eprinomectin, ivermectin etc.),” Olds says.
Because horn flies die within hours of being removed from cattle, non-chemical walk-through traps can be effective if animals pass through it regularly.
Step 3: Eliminate Breeding Grounds
Round hay bales result in significant wastage, which when mixed into the manure-contaminated mud around bales provides a prime breeding site for stable flies.
Olds explains each round bale can produce 200,000 stable flies.
“Reducing hay waste and spreading/drying areas around finished bales is key to reducing stable fly numbers,” she says. “In feedlots, minimizing feed spillage and waste is critical to remove breeding sites for stable and house flies.”
Parasitoid wasps are available from multiple sellers and should be released around fly breeding sites. These are very effective if released before fly populations emerge and released repeatedly through the fly season.
Be careful using insecticides if using parasitoid wasps as they are very small and sensitive to these chemicals. Keeping vegetation surrounding pen areas short and exposed will remove sheltered resting areas, making life more difficult for the flies.
Step 4: Consider Chemical Control Options
Olds stresses chemical control options should be used as a supplement not the basis of a fly control program.
“For horn flies, insecticidal ear tags are an effective method of control if correct rotation is used,” she adds. “Rotate the chemical class of your tag annually, in year one using pyrethroid-based products, year two use organophosphate-based products and year three use macrocyclic lactone tags. Repeating this three-year cycle will reduce the selection pressure on the fly populations, slowing down the spread of resistance.”
Olds also shares these tips for effective tagging: “Tag both ears and place the tag directly into the ear. For the tag to be effective, it must come into direct contact with the animal’s skin, which is greatly reduced when daisy chained.”
She also instructs producers not to tag young calves and adds mature bulls with thick necks might not benefit from tagging unless the tag can touch the skin.
“Although the box may label products as effective for four to five months, field trials have shown that tags only remain effective for 90 to 100 days,” Olds says. “If possible, wait until fly populations are noticeable before tagging animals to get control over peak fly activity period. After 90 days, remove the tag to reduce the risk of insecticide resistance developing.”
To increase coverage, pour-ons of the same chemical class as the ear tag can be used to increase coverage.
“Be aware that a macrocyclic lactone pour-on will impact dung beetle populations,” Olds says. “Make sure animals are dosed accurately according to weight and ensure head to tail coverage. Due to their low contact time with the host and preference for the legs, topical insecticidal treatments are generally not useful against stable flies.”
Spraying the legs can provide some relief, although it should be used sparingly as most sprays are pyrethroid-based, not allowing for effective annual rotation. Baits and premise sprays can be useful in controlling both house and stable flies, look for areas where flies are found resting such as building walls, fence posts and inside sheds and shelters.
Another option is feed through insect growth regulators (IGRs) to control horn fly. Olds says it is important cattle consume the correct amount, which can be difficult under free-choice conditions.
“Under-dosing will result in resistance developing over time, reducing product efficacy,” she says. “Although labeled for stable fly control also, when manure containing the IGR is diluted in the mud and hay, it is no longer effective.”
Often marketed as dung beetle safe, Olds says evaluations of these claims in most species have not been carried out, and their true impact remains unknown.
“Insecticide resistance to IGRs can and does happen; to slow this, rotate annually between Methoprene-based (Group 7A) and diflubenzuron-based products (Group 15),” she adds.
The Veterinary Entomology website, veterinaryentomology.org/vetpestx, provides a searchable database that can help producers select the right products. Producers can select from type of animal, insect and application method.
“For on-animal use, select the best product to allow an annual rotation between pyrethroid (Group 3A), organophosphate (Group 1B) and macrocyclic lactone (Group 6) groups,” Olds says.
Green also recommends using a multi-pronged approach to insect control. He says fly tags, IGR products, pour-ons, back rubbers and dust bags can help diminish the population.
“Both back rubbers and dust bags can be highly effective if managed correctly,” Green advises. “Keep in mind, when these are put out to withstand the elements, including moisture and rain, it’s key to keep the dust fresh or the oil recharged in your back rubbers. Otherwise, they will diminish in their ability to control flies quickly.”
Cammack stresses the importance of accurate dosing by the individual animal’s weight and following label guidelines.
To best control flies and insects on cattle operations, “the easy and effective way is the best way,” Green summarizes. “It’s up to you and with the help of your veterinarian to help create that combination.”
