by Mark Johnson, Oklahoma State University Extension

One of the realities of beef production in Oklahoma is dealing with significant fly populations. The Oklahoma beef cattle industry loses millions of dollars each year due to external parasites. Blood loss, irritation and annoyance lead to reduced levels of performance due to flies. Horn flies, stable flies, house flies and horse flies must be controlled. With an abundance of early spring warmth, recent rains, humidity and warmer temperatures, most of Oklahoma now serves as an ideal breeding ground for these annoying pests that rob profit potential from beef operations.

Getting to know the enemy

The horn fly is the most significant external parasite of cattle, costing the cattle industry an estimated $1.8 billion a year. Although this fly is small and feeds from the back down the side and onto the belly of cattle, it is the sheer number of these flies on a per-animal basis that causes stress to cattle. Considering an individual horn fly will feed on an animal 25 times per day, this will certainly cause significant stress. In a cow-calf system, horn flies on the cow negatively affect weaning weights due to stress causing decreased milk production. This is compounded by the number of flies on the calf.

Stable flies are usually a problem in cattle from March through early May and typically decrease with higher temperatures from June through August (with consistent temperatures above 90° F.) In a typical year, there are two distinct peaks of stable fly populations — one occurring in early April and another occurring in late September.

The stable fly feeds on the front legs of cattle and occasionally on the belly. Their bite is very painful to cattle, causing behaviors such as leg stomping, bunching and standing in water for long periods to avoid the bites.

One of the preferred breeding sites for stable flies is old hay-feeding areas that never dry out and retain moisture for several months. A typical ring/round bale feeding area can provide sufficient habitat for approximately 60,000 stable flies per week. Treatment thresholds for stable flies are 10 flies per animal when observing just the front legs of animals. These numbers will cause significant stress to cows and calves.

Horn flies and stable flies occur in cattle herds across Oklahoma. This means cattle are dealing with both fly pests and those that rely on blood meals as their main food resource. Cattle will need some relief from the biting activity from these fly pests now, and the quickest method is insecticide applied directly to the animals.

Control methods

For stable flies, it is best to find their breeding habitats (hay feeding areas) and clean them up or pull some type of implement through those areas so they can dry out. Consider that a hay-feeding area may not look conducive for fly development, but if you walk on that area and there is moisture seen beneath your feet, it can support stable fly development.

For an insecticide application, the best method is to spray the legs, brisket and belly areas with a product that is labeled for on-animal use. Since cattle will get their legs wet from lying in pastures or walking through water, applying the insecticide with a diesel oil as the carrier will persist a little longer than one applied with water. Cattle producers will have to use a product that can be mixed with diesel and utilize a sprayer with pumps designed for diesel, not water.

For horn flies, there are many different control options. One of the most popular applications for horn fly control is a pour-on product. If using a pyrethroid pour-on, be sure it is synergized with piperonyl butoxide (PBO). The synergist inhibits enzymes that insecticide-resistant flies can develop to detoxify the insecticidal compound. Insecticide-impregnated ear tags are still a viable option for longer horn fly control, but operators will need to rotate the type of product used every year to limit insecticide resistance.

Rotating products is not based on trade names, but by chemical class. For instance, a product can be in three broad chemical classes based on mode of action (the manner in how it kills the fly based on target site). Products labeled for on-animal applications are either pyrethroids, organophosphates or macrocyclic lactones. Veterinarians or county extension personnel can help identify to which chemical class a product belongs based on the active ingredient listed on the product label. Sprays are still a good option to provide some relief to cattle with heavy horn fly infestations. The spray should be applied as directed to the backs, sides and belly of the animal.