February 2010 Articles

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Fly Control Has Been Challenging This Year

Fly Control Has Been Challenging This Year Jeremy Powell, DVM, and Dr. C.A. Tucker, Livestock Entomologist Fly problems started early this year for cattle producers and have continued to be a challenge. Heavy fly infestations can cause stress to your cattle, leading to poor weight gains and decreased milk production. Flies can also spread disease-causing pathogens, leading to pinkeye or mastitis in cattle. Estimated losses from horn flies cost U.S. cattle producers nearly $900 million each year. A USDA report indicated that heavy fly infestations in cows resulted in one-half pound of weight loss per day and a 20 percent drop in milk production. On-the-farm demonstrations conducted in Arkansas showed that beef cows treated with fly tags increased their calf weaning weights between 12 and 60 pounds per head compared to the non-tagged control groups. Cow-calf producers in Arkansas deal primarily with two different species of flies, horn flies and face flies. Horn flies are the most important external parasite of pastured cattle. Both male and female horn flies are active blood feeders and can feed up to 20 times per day. They are generally found on the back and torso of infested cattle. Horn flies remain on cattle during the warmer months of the year, periodically biting their hosts and sucking blood. Infestations surpassing 2,000 flies per animal can be achieved when left unchecked. Their typical life cycle ranges from 9 to 12 days. The females deposit eggs into fresh manure piles. Three larval stages and a pupae stage are completed in the manure pat. Adult flies emerge from the fecal pat and seek new hosts. Producers should rotate from one chemical class to another each year, decreasing the likelihood of resistance development. Face flies are non-blood sucking flies that feed on secretions of the eyes, nose and mouth. Face flies are known to transmit pinkeye bacteria (Moraxella bovis) to cattle. Their life cycle is approximately 12 to 20 days. Females lay approximately 20 eggs per batch in manure. Three larval stages are competed in the manure. The final larval stage will migrate from the manure and develop into characteristic white pupae. Adult emergence follows. Face fly control by itself is probably most effective using dust bags or cattle rubs. Currently, there are many chemical classes of insecticides available for use against external parasites. They include synthetic pyrethroids, organophosphates, endectocides, insect growth regulators, chlorinated hydrocarbons and carbamates. There are a number of useful application methods for these products such as sprays, pourons, spotons, dust bags, back rubbers, boluses, ear tags dips and injectables. Horn flies can develop resistance to insecticide chemicals. Resistance may occur more readily when ear tags are used as the primary control method. This occurs due to the constant exposure of an ear tag chemical to flies throughout several months during the summer. Research has shown that resistance will occur when the same chemical class of insecticide is repeatedly used for two to three years on the same farm. Therefore, producers should rotate from one chemical class of insecticide to another each year, decreasing the likelihood of resistance development. Refer to the chart on below to identify the products that you routinely use in your operation. Using this chart, you can select products from different chemical classes that would allow you to rotate to different classes each year. There are a number of methods that can be utilized by Arkansas cattle producers to help delay the development of insecticide resistance and thereby prolong the effectiveness of chemical insecticide control. These include: 1. Rotate chemical classes of insecticide on an annual basis, and utilize a different application method from year to year 2. Delay applications of insecticide until an economic threshold of flies has been reached (200 flies/animal). 3. Immediately discontinue use of a chemical insecticide when it fails to work, regardless of time of year. Then, utilize a different class of compound. 4. If insecticide ear tags are used, remove them in early September and use an alternative class of insecticide and application method for the remainder of the fly season. 5. Discontinue use of all insecticide at the end of the fly season. For more information about this fly control for cattle, contact your Extension office.