Controlling Flies on Pastured Cattle

Fly Control for Cattle on Pasture in Nebraska

May 2016

photo - cattle in pasture by water sourcePasture fly season is underway and now is the time to consider treatment options for this season. In Nebraska there are three fly species that economically impact pastured cattle: the horn fly, face fly, and stable fly.

The April 2016 video, "Fly Control on Pastured Cattle", highlights management options for flies on pastured cattle.

Horn Flies

It has been estimated that horn flies cost U.S. livestock producers $1 billion annually. Horn flies cause irritation, blood loss, decreased grazing efficiency, reduced weight gains, and a decline in milk production. Additionally, horn flies have been implicated in the spread of summer mastitis.

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Nebraska studies have demonstrated calf weaning weights were 10 to 20 pounds higher when horn flies are controlled on mother cows. Yearling cattle weight gain can also be impacted by up to 18%.

Horn flies have multiple generations per season and the economic injury level (EIL) of 200 flies per animal is often exceeded in Nebraska. To reduce the impact of horn flies, livestock producers should strive to maintain horn fly numbers below 200 per animal during the fly season.

Control methods

There are many different horn fly control methods available to livestock producers; choosing one will depend on your management system.

Force-use, self-treatment devices like dust bags and back-rubbers (oilers) provide effective and economical fly control. However, if used in a free-choice arrangement, expect 25-50% less horn fly control.

Animal sprays can be an effective way of reducing horn flies, but require increased cattle handling, and increased costs and stress to cattle. An effective spray application technology that results in minimal animal stress is to use a mist blower sprayer. Mist blowers do not require animal handling as the mist blower is taken to the field and applications are applied to animals in the pasture.

Oral larvicides (feed-throughs) and insect growth regulators (IGRs) kill horn fly larvae developing in manure pats. To be effective, steady consumption is required and horn fly immigration from neighboring herds can mask the control effectiveness.

Pour-ons are ready to use products applied to the topline of cattle. Nebraska studies indicate pour-ons will maintain horn fly numbers below the EIL for 21-24 days.

Insecticide impregnated ear tags contain one or more insecticide embedded in a plastic matrix. To achieve maximum horn fly control, apply two ear tags per adult animal, and delay tag application until June 1st.

Several new delivery systems for horn fly control have been developed. Insecticide strips (PYthon® and XP820™) have been recently introduced by Y-TEX Corporation. These strips attach to the button side of an existing identification ear tag and contain the same active ingredient as the corresponding insecticide ear tag. The VetGun™ introduced by AgriLabs®, is a CO2 powered device which delivers a capsule that contains 1.5% lamda-cyhalothrin + 7.5% PBO. The VetGun™ can be an effective option for some producers.

Because horn fly populations in Nebraska exhibit some degree of resistance to synthetic pyrethroid ear tags, is important to rotate insecticide classes yearly when using insecticide ear tags and seasonally for other applications.

Face Flies

photo - cow with face fliesThe face fly is a robust fly that resembles the house fly, only slightly larger and darker. It is a nonbiting fly that feeds on animal secretions, nectar, and dung liquids. The female face fly feeding causes damage to eye tissues, increases susceptibility to eye pathogens, and can vector Moraxella bovis, the causal agent of bovine pinkeye.

Control methods

Controlling face flies is essential in reducing most pinkeye problems. Achieving adequate face fly control can be difficult because of the habit of feeding around the face and their limited time spent on the animal.

Control is enhanced when animals receive daily exposure to insecticides from dust bags, oilers, sprays, or insecticide ear tags. Both cows and calves must be treated if control and reduced pinkeye issues are to be reduced.

Pinkeye vaccines are available and should be considered if pinkeye has been a recurring problem. Please check with your local veterinarian about the use of these vaccines in your area.

Stable Flies

photo - stable flies on cows legsStable flies are a serious pest of pasture and confined cattle. The stable fly is a blood feeding fly, mainly feeding on the legs and belly region of animals. The bite is painful and cattle often react by stomping their legs, bunching in corners of pastures, or standing in water to avoid being bitten.

Stable flies cause similar weight losses to both pastured and confined cattle. University of Nebraska research recorded a reduction in average daily gain of 0.44 lbs. per head with animals that received no insecticide treatment compared to animals with received a treatment. Populations of 5 flies per leg are often exceeded in Nebraska pastures.

Control method

The only adult management option available for reducing stable fly numbers is the use of sprays. Sprays can be applied using low pressure sprayers or can be applied with mist blower sprayers. Weekly applications of these products will be required to reduce fly numbers.

Sanitation or clean-up of wasted feed at winter feeding sites may reduce stable fly numbers. If sanitation is not possible, these sites may be treated with a larvicide (Neporex®). But, the application of either procedure may not totally reduce the economic impact of stable fly feeding.

Additional Resource

For current Nebraska control recommendations, please see Nebraska Management Guide for Insect Pests of Livestock and Horses (EC1550, PDF 365KB). The guide and other resources are available on the Department of Entomology's Livestock Entomology page.

When applying any insecticide control product, please read and follow label instructions.

Dave Boxler
Nebraska Extension Educator in Entomology
West Central Research and Extension Center