Horn Fly Control In Cattle

by | Jun 20, 2025 | Beef Cattle, Dairy, Insects, Livestock, Pest Management

Brett Capra, University of Florida, Senior in Animal Sciences & UF/IFAS Extension Intern with Kalyn Waters, UF/IFAS Extension Holmes County

Horn Flies are a significant issue in the Florida Panhandle, especially during the summer months. In hotter temperatures, these flies can develop and reproduce faster, which can result in larger swarms.  With Florida’s warm winters and early springs, these flies seem to be nonstop.

Horn Fly damage is a result of the fly’s blood feeding on cattle, causing irritation and blood loss. Cattle impacted by horn flies can lose 0.3 to 0.5 lbs. in body weight per day. With recent cattle prices, a loss of 0.5 lbs/ day equates to an estimated $1.56 hd/day for a typical beef cattle operation. In a 30-head herd, that would be $46.8 daily or $1,404 monthly. Thus, producers need to gear up for fly season and develop a management plan to mitigate profit losses from Horn Flies as warmer weather sets in.

There are also other risks at play when it comes to Horn Flies. Enough bites in a small area can cause an open wound, which can lead to a secondary infection. Bite lesions, especially if an infection develops, can cause damage to the hide, lowering its value. In addition, Horn Flies have also been shown to cause damage to teats on heifers and have been associated with teat infections and mastitis. This can decrease milk production, which could then, in turn, decrease weaning weight in calves.

Horn Fly eggs are laid in fresh cattle manure (within 10 minutes of dropping), and within 18 hours, the larvae hatch. Development from an egg to a sexually mature fly takes anywhere from 10 to 14 days. Each mature female fly can produce up to 200-500 eggs, with each adult living between 2 and 4 weeks. This short and highly productive life cycle results in a quick increase in Horn Fly populations.

Research indicates that 200 flies/beef cattle (100 flies/dairy cow) is the economic threshold at which implementing fly control is cost effective. In beef cattle herds, fly populations per animal can be easily estimated (Figure 2); however, if cattle seem restless, switching their tails, or kicking at their bellies, there is often enough of an issue to warrant treatment.

Horn Fly populations can be effectively controlled to reduce animal discomfort and to mitigate economic losses for producers. Many methods of Horn Fly control can be implemented in a grazing pasture system. Resistance to treatment is an increasing concern with all pest control in livestock. It is recommended that control methods be rotated between active ingredients to reduce resistance development. For example, if you use pyrethroid Fly Tag X ear tag this year, next year use organophosphate Fly Tag Y.  Fortunately, there are a wide range of products and methods producers can utilize for horn fly control (Table 1), so keep records and make sure you are rotating different classes of insecticides to control this pest.

Spray

Insecticide sprays are used to control flies by drenching a significant portion of the cow’s body. They don’t last as long as other options, requiring you to reapply the spray every few weeks. It is key to cover the entire animal and penetrate the spray to the skin and not just on the hair coat. Sprays work through the skin and hair as well, however since the chemical is diluted with water for application, it is key to saturate the entire animal as the product will not move as effectively though the animals body oil.  In addition, because it is does not bond to the oils on the body, sprays are much more likely to be washed off by rain events.

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Pour On

A liquid drench can be applied to the back line of cattle. While the drench is applied to the back of the cattle, it moves through the oils in the skin and hair to allow for treatment and control over the entire animal’s body. However, this type of control is periodic, resulting in the need for reapplication. In most cases depending on the product used and the weather around time of application, it will be effective for approximately 28 days.

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Insecticide Tags

Tags are placed in cattle’s ears and through grooming and contact with hair coat, the oils from the hair triggers the transfer of the insecticide to the animal. Tags are impregnated with enough chemical to control flies for 3-4 months. If tags are not effectively controlling fly populations after applying, research indicates that you are experiencing a resistance issue. The tags are still controlling flies that are susceptible to the chemical, however the flies that are not being controlled are those that are resistant to the treatment. It is recommended that you remove the tag immediately, otherwise you are allowing resistant flies to be successful breeders, which will increase resistance in that population. Dr. Justin Talley, Oklahoma State, authored a blog article on managing resistance when using Insecticide Ear Tags.  In this publication he said:

“If ear tags are used, the insecticide classes must be rotated. Do not use a pyrethroid ear tag more than once every three years. Do not use an organophosphate ear tag more than two years in succession. Continuous use of ear tags in the same insecticide class will eventually result in horn fly resistance.  Remove ear tags at the end of the fly season or when they lose their effectiveness. Do not tag cattle more than once per fly season, regardless of insecticide class.  If additional horn fly control is needed later in the year, use sprays, pour-ons, dusts or backrubbers. If possible, alternate insecticide classes when changing control methods.”  Dr. Justin Talley, Oklahoma Sate Department of Entomology and Plant Pathology

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Feed Additives

Oral larvicides can be included in supplemental feed such as mineral to control flies. The insecticide is passed through the manure and kills the fly larvae that are laid and develop in the manure. This treatment method is most effective if all the cattle in your area are being treated to reduce Horn Fly populations. Research has shown that flies will travel between 0.5 to 1 mile to find untreated hosts.

Remember to read the label precautions on whichever pesticide you decide to purchase. Make sure to also store pesticides in their original container away from food or feed and keep it out of reach from children, pets and livestock. After finishing with a pesticide, dispose of the empty container promptly and with care.

Horn Flies are an economically important pest that cattle producers must manage on an annual basis. The good news however, is that you still have a variety of effective methods available to mitigate profit losses caused by them. Dr. P. E. Kaufman is an expert in Horn Fly management, formerly at the University of Florida, and now serving at Texas A&M. He encourages producers to “manage the population, don’t try to exterminate them”.  In an effort to provide producers with tools to help do so, he collaborated in a multi-state effort to develop an online system for obtaining the names of registered pesticides appropriate for use with livestock and pets.

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Additional information about Horn Flies can be found at ENY288/IN952: Horn Fly Management

Kalyn Waters
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