– John Yost, OSU Extension Educator, AgNR, Wayne County
Horn flies are considered the greatest pest of pastured cattle.
The increase in temperatures is also bring with it an increase in flies. Flies, if left unmanaged, can present a significant challenge to the welfare and production of all our livestock species. Fly control is not a one-and-done treatment strategy. They require season long management, that may require a variety of approaches to seasonally address. The three main types of flies that we are concerned about are face, horn, and stable flies. The species have similarities but also some subtle differences that you need to take into account when selecting potential control options.
Horn flies are the most economically damaging species for livestock. Research has shown that calf weights can be reduced by 4 to 15% and replacement heifer weights of up to 18% when populations reach a threshold of 200 flies/animal. Milk production, for dairy cattle, can be decreased by up to 15%. Horn flies are blood feeders and will consume about 30 meals per day. They spend the majority of their time on the animal and will congregate along the withers, back and sides. Females will only lay eggs in fresh manure, where the eggs will hatch and larva mature.
Face flies utilize a sponging type mouth, with prestomal teeth, to rasp, scrape, and penetrate tissue to feed on secretions. They will most likely be found, as the name implies, on the face and any open wound. They spend little time on the animal but can be a vector to transmit pinkeye and IBR. Females also lay their eggs in fresh manure and are more of a pasture problem. They can produce 3 to 4 generations each year.
Stable flies are believed to only spend between 2 to 5 minutes on an animal each day. They consume one blood meal and will spend the rest of their time out of the sun in barns or trees. Unlike the other species, females prefer to lay their eggs in soiled bedding, algal mats, wet grass clippings, and older manure piles. Their bites are very painful to livestock causing general irritation which may lead to reduced feed consumption and subsequent performance.
Adequate control will vary dependent on where your livestock are housed and other management factors. Again, fly management is not a one application and done process. Consequently, a monthly, or more frequent, comprehensive management strategy will need to be deployed to keep populations at bay. Due to their relatively short lifespan, the most effective seasonal control should focus on limiting larval development and controlling breeding sites. For confinement housing situations, facility sanitation is a key control factor. Timely removal of manure and soiled bedding is crucial to limiting populations. Careful attention to bunk management and cleaning up spilled feed will also reduce potential breeding sites.
In addition to facility sanitation, larvicides and fly predators are other tools available to producers to lower fly populations. These products do not kill adult flies, but stop larval development, or in the case of the predators feed on growing larva. There is a multitude of feed through larvicides that can be added to your TMR or provided with your mineral supplementation to prevent larval development in the animal’s manure. Although they will not control adult flies, they will reduce populations over time. The fly predators are parasitic wasps that feed on growing fly larva. They are not a pest to livestock or humans and can be extremely effective if used properly. Species have been developed for different production systems. They can be used around confinement operations or in pasture situations. The manager will get a shipment of new wasp eggs every couple of weeks. Typical instructions are to wait for 2 to 7 days after receiving your shipment, which allows for some of the parasites to hatch in the bag and then the contents can be spread around the barn, across a pasture, or in areas were the livestock may congregate for long periods of time (i.e under shade trees or around waterers).
To control adults, topical insecticidal products are available. These can be applied to livestock as a pour on or can be applied via face or back rubbers. Insecticidal ear tags are also very effective in controlling face flies. Whenever using chemical control methods, thought should be given to control potential pest resistance. Fly populations have shown resistance to many of the organophosphate insecticides. Producers should read the product label and remove/replace eartags based on manufacturer recommendations. Producers should also be aware of any meat or milk withdrawal restrictions provided on the product label.