Mark Z. Johnson, Oklahoma State University Extension Beef Cattle Breeding Specialist
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 or horse flies must be controlled. With 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.
Horn flies are the most significant external parasites of cattle causing an estimated $1.8 billion impact on the cattle industry as a whole annually. Although this fly is small and feeds from the back down the side and onto the belly of cattle it is the sheer numbers of these flies on a per animal basis that cause stress to cattle. Considering the number of times an individual horn fly will feed on an animal throughout the day is 25 times per day then those numbers will certainly cause significant stress to cattle. In a cow – calf system the horn flies on the cow or heifer impact weaning weights in calves due to the impact of that stress causes decreased milk production but when combined with direct fly numbers on the calf then the impact can be greater.
Stable flies are usually a problem in cattle from March through early May and typically decrease when temperatures increase from June through August. The stable fly preferably feeds on the front legs of cattle and occasionally on the belly of animals. Their bite is very painful to cattle causing significant behavioral reactions 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 are old hay feeding areas that never dry out or retain moisture for several months. In fact, 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 both the cow and calf but the stable fly populations will decrease if humidity levels begin to decline with consistent temperatures above 90°F. In a typical year, there are two distinct peaks of stable fly populations with one occurring in early April and another one occurring in late September.
Horn flies and stable flies are on cattle herds across Oklahoma. This means cattle are dealing with both fly pests and 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 are insecticides applied directly to the animals.
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 then 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 laying in pastures or walking through water then 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 options to control this pest. One of the most popular applications for horn fly control are pour-on products. If using a pyrethroid pour-on be sure that 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 the chemical class the product belongs in. For instance, a product can be in three broad chemical classes based on its mode of action (the manner in how it kills the fly based on target site) and products labeled for on-animal applications are either pyrethroids, organophosphates, or macrocylic lactones. Veterinarians or country extension personnel can help identify which chemical class a product belongs based on the active ingredient listed on the product label if assistance is needed to identify the chemical class. Sprays are still a good option to provide some relief to cattle with heavy horn fly infestations and the spray should be applied as a course spray that is directed at the backs, sides and belly of the animal. Insect growth regulators (IGR) that are feed through mineral are a very good option when combined with other control applications whether it be ear tags, pour-ons or sprays but producers will need to monitor consumption to be sure that the herd is averaging ~4 oz. / hd/ day to prevent flies from developing from the manure pats. Self-application devices such as oilers can be effective if you make it a force use system or put multiple oilers out to ensure the whole herd is treated properly. A typical force use system is setting it up where cattle have to go under the oiler to get to water or a feed area. Regardless of the type of insecticide application chosen it important to get cattle treated to provide some relief from the biting flies so that cattle are not stressed especially when you add the additional heat stress that becomes a factor with high heat indices.
Justin Talley talks about the importance of managing horn flies on a SunUP TV episode from August 17, 2019. https://www.youtube.com/watch?v=BiKY5LX8ZnY