Fly Control for the Beef Herd

B. C. Allison

The necessity for a fly control program for beef herds is inevitable and now is the time to plan your's for this year. The two major species of flies that cause the most serious decreases in beef production and require the most control efforts are the horn fly and face fly. The horn fly alone is estimated to cause animal losses to the U.S. beef industry of $700 million. Tests have shown that the annoyance, irritation and blood loss caused by flies can reduce weaning weights of calves nursing fly infested mother cows by 12 to 14 pounds; average daily gain of grazing yearly steers may be reduced 12 to 14 percent, or as much as 30 pounds during the grazing season. Both face flies and horn flies annoy cattle, resulting in reduced grazing time and increased energy expenditure.

The adult horn fly, which is about one-half the size of a house fly, has piercing/ sucking mouth parts and feeds on blood and tissue fluids of cattle. They spend most of their adult life on cattle and feed 20 to 40 times a day. They are normally found on the animal's back, but may migrate to the sides and the belly as the temperatures increase. They are weak fliers, but may be carried great distances by high winds. The females leave the animal to lay eggs only in fresh cow manure, where they hatch into larvae. The life cycle is completed in eight to 45 days depending on temperature and humidity. With the short life cycle they may complete a dozen or more generations during the warm months. The fact that adult horn flies spend most of their time on cattle makes their control much easier.

The face fly is about the size of a house fly. They are non-biting and feed on secretions from the eyes and muzzle. They avoid entering dark places, such as a barn, while on the animal. The female lays eggs on freshly deposited manure like the horn fly; however, unlike the horn fly they are present on cattle only about 10 percent of the time and may be found resting on fence posts, trees, bushes and other objects the other 90 percent of the time. Because they spend so little time on the animal and do not feed on blood they are much harder to control than horn flies. When feeding around the eyes, they cause irritation creating an environment suited to bacterial growth. As the eye becomes irritated and begins to weep, it attracts more and more flies, adding to the irritation and opportunity for spread of infection. In addition to being an annoyance to the animal they are thought to be spreaders of bacterial organisms that cause pinkeye.

Other flies common to cattle are the house fly, which feeds on organic matter, and the stable fly, which feeds on blood. The females of both lay eggs in freshly deposited manure and other types of decaying organic matter. Female horse flies and deer flies feed on blood of warm-blooded animals while their male counterparts feed on vegetable sap, etc. The females lay eggs on foliage or other objects that project over water or moist ground. Because these species of flies lay eggs in places other than cow manure oral larvicides do not give good control.

Cattle can tolerate low horn fly populations. When horn fly populations reach 100 to 200 per animal it is economically advantageous to begin a control program. There are several methods of fly control, such as insecticide sprays, dusts, pour-ons, oilers, dust bags, ear tags, oral larvicides in minerals and blocks and controlled release boluses. All of these methods are effective and have a place in the control program; however, the best fly control can most likely be obtained through an integrated fly control program.

In an integrated fly control program two or more products that compliment each other are used. One product should give good control where the other may be weak, thus reducing the probability of flies developing insecticide resistance. Many cases have been reported where flies developed resistance to insecticides that were very effective when first introduced. A good example are the organophosphate and pyrethroid ear tags that were very effective when first introduced several years ago. This resistance most likely developed as a result of continued exposure of the fly population to the same insecticide or same family of insecticides and/or exposure to less than lethal levels of the insecticide.

To combat this development of resistance to insecticides a producer should consider using another method of fly control, such as sprays, dusts, pour-ons, oral larvicides, etc. in the early part of the fly season, then putting slow release insecticide ear tags (containing a different family of insecticides than in the products used earlier), in later (early June). This will extend the effectiveness of the ear tags further into the fall. Two tags should be applied per animal to insure that a lethal dosage of insecticide is delivered.

Another fly control management practice that should be implemented is to cut out old ear tags in the fall to eliminate the chance of flies being exposed to sub-lethal dosage of insecticide and developing resistance. There are many brands of insecticide ear tags on the market; however, many of them have the same insecticide or family of insecticide impregnated in them. When choosing ear tags you should select a tag that contains a different insecticide from that contained in the tags used the previous year to reduce the possibility of an insecticide resistance developing.

Most producers seem to be familiar with the use of sprays, dusts, pour-ons, ear tags, and self-applicating devices. The sprays, dusts and pour-ons only give effective control for a specified period of time after application. Self-application devices should be located where cattle are forced to go through to obtain water or salt to insure daily usage. They should not be allowed to run out and the type of insecticide used in them should also be rotated to avoid development of resistance. Dust applicators should be protected from rain to avoid caking. The pour-on systemic insecticides are effective for a period of time on flies that feed on blood. Another means of fly control is oral larvicides which may be obtained in several different carriers, such as free choice minerals, blocks, etc. These products, when fed, pass through the digestive tract of the animal and kill developing fly larvae in the manure or inhibit their development. They are not effective against adult flies and, for this reason, if cattle not receiving an oral larvicide are located close to your herd, you may still have fly problems.

Another type of fly control is the controlled release bolus. The bolus settles into the reticulum where a controlled dose of chemical is released in the manure. It is an insect growth regulator and prevents the immature insects from becoming adults. Similar to oral larvicides, if a nearby herd does not use the oral larvicide or controlled release bolus, you may still experience fly problems.

Other methods of fly control which have been developed and may be used more in the future are fly traps, sex attractants, sterile male flies and predator wasps. Monitor the effectiveness of your fly control program and supplement it with another method or insecticide during the season as necessary. The best method of fly control is the integrated approach, using several different methods and insecticides for a longer lasting, more effective fly control program.

Animal Husbandry Newsletter May 1996
Department of Animal Science, North Carolina State University
Published by North Carolina Cooperative Extension Service, North Carolina State University, Raleigh, North Carolina
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
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