Controlling Flies On Cattle Requires Proper Timing

Face flies, horn flies and stable flies are the most common and most treated pests on North Dakota livestock operations. Left uncontrolled, these pests can cause significant loss in livestock production.

Fortunately, North Dakota State University Extension specialists say that the proper pest management strategy can provide effective control.

While integrated pest management is commonplace for controlling crop pests, similar concepts can apply to controlling livestock pests, according to Extension veterinarian and livestock stewardship specialist, Dr. Gerald Stokka.

"Integrated pest management involves using the right type of control at the right time for the right duration to control pests effectively," Dr. Stokka says. "For example, in beef cow-calf operations, applying pest control for lice and flies prior to pasture turnout will not be effective and will waste resources related to pest control."

Timing and type of pest control depends on the species of flies. Horn and face flies typically are not present at pasture turnout and do not reach economic thresholds for applying control until midsummer.

Horn flies are gray and look like small houseflies. Horn flies bite and spend most of their time clustered around the head, shoulders and back of cattle. These blood-sucking flies feed up to 20 to 30 times per day. This constant biting causes cattle pain and stress, and can reduce the cattle's weight gains by as much as 20 pounds, according to Dr. Stokka.

Face flies look like large, dark house flies. They are nonbiting flies that feed on animal secretions, plant nectar and manure liquids. Face flies may transmit pathogens responsible for infecting the eye and causing pinkeye in cattle. The life cycle of a face fly is approximately 21 days. Populations tend to peak in late summer.

Stable flies are similar in size to house flies, but have circular markings that distinguish them from horn flies. In addition, these flies bite on the abdomen and legs, feed on blood, and are very disruptive to cattle grazing. They breed on organic matter and are very difficult to control with topical pour-on and injectable products.

Pest density is another factor in determining timing of control strategy, according to Colin Tobin, animal scientist at the NDSU Carrington Research Extension Center.

"When fly counts reach 200 flies per animal, the economic threshold has been reached and animals will have significant weight loss," Tobin says. "The economic threshold is the pest density at which producers should take action to manage the pest."

Tobin says that the first step in determining when to apply control is to properly scout pastures and cattle to determine fly type and fly populations. Horn flies typically rest on cattle throughout the day, whereas face flies land on the face of cattle for a meal and then retreat to nearby structures (forages, fences, etc.).

Ear tags contain insecticides that are released slowly into the animal's hair by movement, so ear tags should not be applied until fly populations are nearing the economic thresholds (typically from mid-June to July). Tobin advises reading insecticide labels carefully because recommendations can vary for the number of tags to apply (one or two), the age of cattle that can be tagged, and the chemical class of active ingredient (pyretheroid, organophosphate or a combination).

NDSU Extension specialists recommend rotating the class of insecticide each year and removing tags when they no longer provide effective fly control to help prevent flies from becoming resistant to the insecticides.

"To achieve proper fly control, pour-on and sprays must be applied every two to three weeks throughout the fly season," Tobin says. "Applying these products before pasture turnout likely will not be an effective fly control method. Additionally, all avermectin pour-ons and injectables impact internal parasites and are not labeled for fly control."

Feed additive insecticides can be included in mineral formulations for the cattle. The additives pass through the animals' digestive system and destroy the developing horn fly maggots in the manure. These additives are effective in killing 80% to 90% of the developing fly larvae in animals that have consumed the product.

Extension livestock specialist Karl Hoppe advises ranchers to offer feed additives at least 30 days prior to fly emergence in late June or early July. Continuous use of these products may speed up resistance in the fly populations, he warns.

Back rubbers, dusters and other means of delivering insecticides, as well as nonchemical fly traps and reliance on natural fly defense mechanisms (dung beetle control of larvae), also are available. As with the other control methods, Hoppe advises watching for economic thresholds and considering what control measure will work best.

"When applying any type of pest control, be sure to carefully read the label prior to application," Hoppe says. "It is important to monitor populations to see if the product is achieving the desired level of control."

If a product is not effective, the fly population may have developed a resistance to that type of insecticide, which may require another method or product.

"Pest control can be costly," Hoppe says. "Producers can reduce costs by following principles of integrated pest management and applying the appropriate products at the appropriate time for the appropriate control of pest populations."