Matheus Ferreira, Ashley Edwards, Marcelo Vedovatto and Lee Faulk

Fly management is a constant challenge for cattle producers in the southeastern United States, where warm and humid conditions favor rapid increases in fly populations. Numerous studies by LSU AgCenter researchers and other scientists have shown that fly infestations affect the productivity and profitability of cattle operations throughout the U.S., making flies one of the costliest external parasites in livestock operations.

National estimates place annual economic losses from horn fly infestations for cattle production at approximately $876 million. For stable flies, data published in the Journal of Medical Entomology in 2012 estimated a total impact to U.S. cattle industries of $2.2 billion per year, which includes dairy and beef cattle. Implementing effective fly management strategies not only enhances cattle health and welfare but also significantly improves production efficiency. In this article, AgCenter researchers and extension experts discuss practical approaches to fly management, focusing on the timing of interventions and the measurable impacts these practices can have on cattle growth and well-being.

A leading researcher of livestock flies was Lane Foil, an entomologist with the LSU AgCenter. He died last year after a brief illness. Learn more about him in this edition of Louisiana Agriculture.

Understanding the Types of Flies Affecting Cattle

In the southeastern U.S., cattle are primarily affected by horn flies, stable flies and face flies. Among these, horn flies are the most economically damaging insect pest of grazing cattle.

Illustration by Ana Iverson

Horn flies are blood-feeding flies usually found on the back, sides and poll area (the space between the ears where horns may grow) of cattle, causing irritation, blood loss and reduced grazing efficiency. Each fly can bite up to 40 times a day, leading to significant discomfort and energy loss for the cattle (Figure 1).

Stable flies can deliver painful bites, primarily feeding on the legs and causing cattle to bunch together to avoid being bitten, which can lead to increased heat stress and reduced feed intake (Figure 2).

Face flies, as the name suggests, are nonbiting flies found around the face area that feed on secretions from the eyes, nose and mouth. They can spread diseases like pinkeye, causing significant health issues and decreased productivity.

Producers have many fly control options and strategies available to help manage these three fly species, which economically impact grazing cattle.

Impact on Cattle Health and Welfare

Effective fly management has profound impacts on cattle health and welfare because flies are vectors for several diseases, including pinkeye and anaplasmosis. Face flies are the main cause of pinkeye and spread the bacteria from one animal to another as they feed on eye secretions. Pinkeye is a highly contagious bacterial infection affecting the eyes of cattle and is also known as infectious bovine keratoconjunctivitis. It can cause pain and discomfort, leading to decreased grazing and feed intake and, consequently, reduced growth rates. Horn flies are generally not considered to be important vectors of cattle diseases, but they are the intermediate host for a nematode that causes skin lesions in cattle.

Welfare plays an important role in productivity because comfortable cattle are more productive. Reducing stress and irritation from flies leads to improved welfare, as cattle spend more time grazing and less time fighting fly annoyance. While fly management is a necessity anywhere in the U.S., hot and humid conditions make the practice even more necessary. As summer days arrive, fly populations peak along with temperature and humidity. Stable fly-infested cattle tend to bunch up to avoid being bitten, which leads to heat stress and, therefore, less productive cattle. Managing fly populations reduces the incidence of diseases, improves herd health and welfare, and reduces veterinary costs.

Impact on Cattle Growth and Economics

Efficient growth and production are essentially associated with healthy, less stressed cattle that can express natural grazing behavior and utilize nutrients more efficiently. This leads to better feed intake and conversion rates, which result in improved weight gain and overall productivity, according to a 1992 study published in the Journal of Animal Science.

Studies conducted in the U.S. and Canada have shown that cattle with effective fly management can gain 15% to 30% more weight compared to those not treated. One of these studies, a 1995 horn fly management study by AgCenter researchers, found that over a three-year period, treated cattle with 25% to 50% Brahman heritage gained 17% more than untreated cattle. In a scenario where fly-treated steers gain 30% more weight during the background phase (post‑weaning growing period before finishing) gaining 1 pound per day versus 0.70 of a pound, for example — the effect is substantial. In today’s market, depending on the fly-control program, producers can expect a return of $20 to $40 for every $1 invested in fly management. This estimate is based on an additional 20% to 30% weight gain during the June to September backgrounding period using the current average price of $3.40 per pound for 600-pound steer calves.

Average daily gain differences are variable among studies and highly influenced by location, breed and year. However, an overwhelming number of studies consistently find significant differences between treated and untreated cattle. Differences in performance between treated and untreated cattle also extend to cow-calf pairs. A four-year study conducted in New Mexico on rangelands showed that fly-treated cows gain, on average, 33 pounds more each year in comparison to untreated cows. Furthermore, calves paired with treated cows were 35 pounds heavier at weaning compared to calves paired with cows infested with horn flies, according to the New Mexico State University study published in 2019. Similarly, studies conducted in Nebraska have shown that calf weaning weights were 10 to 20 pounds higher when horn flies were controlled on nursing cows, according to a 1984 study published in the Journal of Economic Entomology.

Although fly management can impact the growth performance of heifers, it does not seem to have a strong impact on reproduction. A 2003 study conducted by AgCenter researchers with 670 Angus and Brangus heifers showed that the total weight gain of treated heifers was 14% greater than that of untreated heifers. However, the fly treatment did not affect pregnancy rate (78% and 75% for untreated and treated heifers, respectively). Fly management also plays an important role in dairy operations, as milk production can be reduced by 10% to 20% if cows are not fly-treated, according to a 1958 study.

Control Methods

A multifaceted approach is essential for effective fly control. Flies can be directly or indirectly controlled. Direct control measures are a combination of efforts directed to eliminate flies, such as the use of insecticides and traps, whereas indirect control is essentially the implementation of practices to reduce the ambient spreading of flies.

Indirect Control (Cultural Management Practices)

Implementing practices such as regular manure management reduce breeding sites for flies. Keeping areas where cattle congregate clean and dry is vital. Additionally, rotational grazing can minimize the buildup of fly populations in specific areas. Accumulations of hay and animal waste around these feeders are excellent substrates for the breeding and development of stable fly larvae, which may be the primary source of stable fly infestations in Louisiana.

Direct Control (Insecticides and Traps)

For direct elimination of flies, popular options include pour-ons, sprays, dust bags and ear tags. It is imperative to use a combination of insecticide classes to prevent resistance. The best product for your operation is the one that delivers the best results. A product that works well for one producer may not fit your operation’s needs. Therefore, it is important to thoroughly evaluate the effectiveness of control methods in your own system and adapt accordingly. Rotating products and following label instructions are essential to ensure long-term effectiveness. In addition to insecticide treatments, using fly traps, sticky tapes and other physical barriers around working facilities and feeding areas help in controlling fly populations.

Feed-Through Larvicides/Insect Growth Regulators (IGRs): These products prevent fly larvae from maturing into adults and are most effective against horn flies and face flies. They can be delivered through feed rations, supplements or mineral mixes formulated with fly control. IGRs are designed to disrupt the growth and development of the fly larva. Several commercial options are available, and the best choice depends on your operation’s budget and target species. The IGRs are not a must in fly control measures but are definitely helpful in controlling flies before they peak. To stay ahead of this cycle, IGRs should be included in mineral or feed supplements starting in late February to early March at least 30 days before fly emergence. This timing ensures the active ingredient is already present in manure when the first flies begin reproducing, interrupting their life cycle and reducing the number of adult flies later in the season.

Garlic blends: These products may include garlic powder, garlic oil, citronella or peppermint, which act as natural fly repellents. They are typically added to mineral mixes or feed and do not kill flies directly. Instead, once ingested, garlic compounds are released through the animal’s skin and breath, creating an odor that discourages flies, lice, mites and other biting pests, particularly around the eyes and nose. Effectiveness usually develops within two to four weeks of consistent intake. Producers can purchase premixed garlic mineral or add about 2% garlic powder to mineral or salt mixes. For best results, garlic should be used together with other larvicides or pesticides. In a Canadian demonstration project (Beacon Hill Community Pasture), cows receiving garlic-fortified mineral salt averaged 55% fewer flies than those fed regular trace mineral salt during the summer.

Insecticide ear tags: Insecticide ear tags are insecticide-impregnated tags that can be applied to cattle. These types of fly tags are the only fly treatment that gives sustained long-term control. Some ear tags can protect for up to five months for horn flies and up to four months for face flies on cattle. Choose tags containing active ingredients that are different from those used in previous years to prevent resistance. Remove ear tags at the end of the fly season or when they lose their effectiveness, and do not tag cattle more than once per fly season, regardless of insecticide class. Heifers, cows and weaned calves can receive fly tags, whereas the use of insecticide ear tags for bulls and nursing calves is not recommended.

Topical insecticides: Pour-on or spray-on insecticides are usually easy to apply, do not require mixing and can target specific fly species. Insecticides should be used in an integrated pest management system, which may involve repeat treatments and the use of other pest control practices. Repeat applications must be administered according to product instructions and infestation levels. Always follow the guidance and information on administration and dosage, preslaughter withdrawal and milk discard.

Dust bags and back rubbers: Dust bags are cloth bags filled with insecticidal dust, while back rubbers are long ropelike or fabric-covered devices that are soaked in an insecticide solution. They are usually hung in areas where cattle naturally walk through, like near water or feed sources. As the cattle brush against a back rubber, the insecticide is applied to their skin to help kill or repel pests. These are effective methods and allow insecticides to be applied to cattle without the need for direct handling. It is important to install and maintain dust bags and back rubbers treated with appropriate insecticides at entry points to water and feeding areas to ensure regular use by cattle.

Understanding the Active Ingredients

Producers often hear the advice, “You need to rotate your fly control products.” What this really means is not just switching brand names, but rotating active ingredients or chemical classes used to kill flies. This is likely one of the most important points to understand before putting together a fly control program. There are many products on the market with a wide range of active ingredients. Many of these products share similar active ingredients or belong to the same chemical family. For example, permethrin and cypermethrin are different ingredients, but both belong to the pyrethroid class. If flies become resistant to one, they will likely resist others in the same group. Some products are boosted with piperonyl butoxide (PBO). PBO is a synergist that improves insecticide effectiveness by blocking insect detox enzymes. It is not an insecticide alone, but it helps reduce the resistance of flies to the insecticide. A good strategy is to use different chemical classes for tags and pour-ons within the same season, and to rotate classes each year (for example, using pyrethroids for one year and organophosphates the next). This approach helps maintain product effectiveness and ensures better long-term fly management.

Did Your Fly Management Program Work Last Year?

As previously shown, cattle left untreated against flies are significantly less productive during peak fly season. Implementation of effective fly management is important to maintain herd productivity, efficiency and economic value. The economic injury level for horn flies is 200 flies per animal, which means that 200 is the standard threshold for treating cattle. For stable flies, no threshold is set, but research has shown that an average daily count of 25 to 50 flies per animal will have an economic effect on cattle, whereas others have shown that an average of only two flies per leg could reduce weight gain in heifers.

Based on the direct and indirect control methods described above, the following key timing of interventions are recommended for the Southeastern U.S. (Table 1). These are tips and guidelines for implementing an effective fly management program in your operation. However, not every single step is necessary for every production system, so measures need to be taken according to current necessities.

Final Thoughts

In the southeastern U.S., where fly populations are particularly problematic, starting early and maintaining consistent control efforts through the summer is essential. Effective fly management consists of multiple strategies that combine the correct timing of insecticide applications, physical barriers and sanitization. Each fly control method has advantages and disadvantages that should be considered during decision-making. By investing in fly control strategies, cattle producers can enhance the welfare and performance of their cattle, leading to a more profitable and sustainable operation.

Matheus Ferreira is an assistant professor based at the LSU AgCenter Hill Farm Research Station in Homer. Ashley Edwards is the state livestock extension specialist based at the AgCenter Dean Lee Research Station in Alexandria. Marcelo Vedovatto is an assistant professor of beef cattle nutrition based at Dean Lee, and Lee Faulk is an associate extension agent focused on animal production, beef cattle and forage.

This article appears in the winter 2026 edition of Louisiana Agriculture.

Flies gather around the feet of cattle. Photo by Matheus Ferreira

An Angus-cross cow is loaded with horn flies in the beginning of summer in northwest Louisiana. Photo by Matheus Ferreira.