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Flies and Pink Eye a Problem Again This Summer

By Ric Bessin and Jonathan L. Larson; UK Entomology Extension Specialists

Face flies are annoying pests for cattle that can impact the animal’s welfare by just constantly molesting the eyes of our animals. These flies are looking to feed on tears but will also feed on saliva, blood, and nasal discharges. They do this by using their unique mouthparts, which resemble sponges and help them consume their liquid foods. Recently, county Extension agents informed us that they have received a large influx of questions regarding the connection between these pests and their transmission of pink eye.

Identification & Life cycle

Face flies look very similar to house flies in shape and coloration but are slightly larger than their close relative. They are dark grey with four black stripes that run down their back. As with a lot of flies, the maggots develop in fecal material. Specifically, face fly maggots develop in freshly deposited cattle manure. The maggots will hatch from eggs and then go through four stages of development over 15 to 25 days, depending on the weather. During the summer, face flies are not often found in structures, but the adults do overwinter in barns or attics and will become active again in the spring to start the next generation of flies.

Figure 1: Face flies are in the same genus as house flies and look very similar to that species. They are slightly larger in comparison and are less common in structures in the summer. Adults can be found resting on plants and fences when not on animals. (Photo: Whitney Cranshaw, Colorado State University, Bugwood.org)

Pink Eye Transmission

High numbers of face flies are associated with higher rates of pink eye issues. The feeding style of the flies causes more avenues of introduction by scratching the eyes, and the flies have been demonstrated to carry the causative agent of pink eye as well. Some estimates put the cost of pink eye in cattle at about $150 million annually.

Figure 2: Face flies feed on tears they induce from the eyes of cattle. The feeding style of the flies leads to irritation and can open the eyes up to infection by pathogens, in particular pink eye. (Photo: Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org)

Management Must Be Multifaceted

Fly control is essential, but can be difficult as face flies are only on the animal for a small percentage of the time. Therefore, addressing the egg and larval stages of the fly, as well as the adults, is most effective. A moderate to heavy fly infestation is when there are 10 to 20 flies per animal during the middle of the day. A single fly-control program will not work on every farm, so it often takes multiple tactics of control to achieve good results.

Fly tags (mid- to late May, through mid-September-October)(one ear tag or session or two sessions; be sure to use the number of tags required by the manufacturer), insecticide pour-ons, back rubbers (no 2 diesel), dust bags and knock-down sprays (Bachpack or ATV) are helpful in reducing the number of adult face flies on your animals. Fly traps in barns can also be helpful in reducing the number of flies. Feed additives with insect growth regulators are available that target the maggots that are laid in the manure. Encouraging dung beetles, which break down the manure pat, will also decrease egg survival.

Face flies can develop resistance to pesticides over time, so switching the drug mode of action of pesticides used every year is important. For example, if pyrethrins are used one year, then organophosphates should be used the following year. Waiting until the start of fly season to apply fly tags and removing the old fly tags in the fall also decreases the development of resistance. It is also extremely important to follow the safety precautions recommended by the manufacturer, as these insecticides can be toxic to people if handled improperly.

Appropriate grazing, along with clipping pastures will prevent seed-head development, reducing the irritation to the eyes of cattle, as well as reducing the resting areas for the flies. Clipping pastures to a low stubble height in May just after the seed heads emerge and again in mid-summer when weeds appear is recommended. Shaded areas need to be available to decrease the ultraviolet (UV) exposure and, in Herefords, breeding for pigmented eyelids has been successful, as this is a heritable trait. A good management program, including an appropriate vaccination program [especially infectious bovine rhinotracheitis (IBR) and bovine viral diarrhea (BVD)] and having good quality nutrition and minerals available at all times, will improve the overall condition of the cattle and decrease the incidence of this disease. Overhead hay feeders should be lowered and round bales should be rolled out. Ensuring adequate bunk space will decrease direct contact between the animals. Animals that develop pinkeye should be isolated if possible.

Late Summer Cattle Fly Check Can Catch Control Breakdown

Horn fly and face fly numbers will continue to build for a few weeks, which will put pressure on control programs. It is a good time to evaluate the pasture fly situation in your herd; check during the early afternoon on a sunny day (Figure 1). Less than 100 horn flies per side and less than 10 face flies per head is a good target for animal protection. Consider an adjustment or supplemental measure if fly numbers exceed these guidelines.

Figure 1. Evaluate horn fly and face fly control (Photo: Lee Townsend, UK)

Management

Late season fly control is important. Pasture flies are approaching peak numbers for the season, so their impacts are near maximum levels. Also, exposure of flies to less than recommended rates of insecticide due to less effective treatment selects for resistant individuals and increased chance for control failure.  To ensure flys are kept in check, evaluate management options by following suggestions:

Ear Tags

Insecticide-impregnated cattle ear tags can provide 12 to 15 weeks or protection. Effectiveness may be running out in herds that were tagged a little early in the season.

Feed-thru Insecticides

Feed-thru insecticides in mineral supplements require a minimum level of daily consumption by each animal. Be sure that the product is available and that the consumption rate appears to be on-target. This alternative is based on controlling horn fly and face fly maggots that develop only in cow manure. Face flies and horn flies can move a mile or two, so action may be needed to control flies that move in from nearby herds. Provide supplemental control, as necessary.

Figure 2.  Mineral feeder with fly wipe (Photo: Lee Townsend, UK)

Self-applicators

Be sure that self-applicators are charged and working. The fly wipe in Figure 2 appears to be dry so the reservoir tank may need to be filled. In some cases, dust can build up enough to reduce the wicking action in wipes and oilers. Be sure dust bags have not been damaged and that the insecticide in them is dry and flowing.

Pour-on

Pour-on and spray applications generally provide about 4 weeks of fly control. Check the last treatment date and be sure doses are measured accurately.

 

By Lee Townsend, Extension Entomologist