When developing strategies for horn fly control, it is important to distinguish among horn flies, stable flies and house flies.
Horn flies are smaller than both stable and house flies and are generally found on the backs or sides of cattle. During the heat of the day or if conditions are windy, horn flies will move to the belly of cattle. In contrast, stable flies will be found on the legs of cattle. Cattle grouped in a circle, especially in the spring, can be another indicator of stable flies. Cattle on the edge of the group will try to move toward the middle to get relief from stable flies. House flies are generally seen around the eyes and nose where they feed on mucus secretions.
Horn flies can be found resting on cattle except when they are laying eggs in or just under fresh manure patties. In contrast, stable and house flies are only found on cattle when they are feeding.
There is no perfect control strategy for horn flies. The most effective control strategies generally involve the use of both a feed-through product and a topical insecticide. The remainder of this month’s column will focus on feed-through options.
There are three common active ingredients used in feed-through formulations: methoprene, diflubenzuron and tetrachlorvinphos. Insect growth regulators like methoprene and diflubenzuron don’t kill the adult flies but reduce fly numbers by preventing eggs from developing into adults.
Common self-fed products that contain one of the above active ingredients include loose minerals, tubs, liquid feed and blocks. For feed-through products to provide the most benefit, it is critical that the right dose is used and that cattle routinely consume enough of the product. Check the feed tag on the product for the dose and the recommended intake.
If using a feed product with methoprene, diflubenzuron or tetrachlorvinphos, it is best to start feeding these products early in the year. For producers in the southern part of the country, it may make sense to feed these products throughout the entire year.
If pastures need to be sprayed for small armyworms or grasshoppers, check the label to see if the product being considered may also help suppress fly numbers. Some products that contain diflubenzuron are labeled to control armyworms, grasshoppers and suppress horn fly emergence from manure patties for two weeks or longer.
