How Fly Spray Works

Although fly spray is a familiar product to horse owners, you may not have given much thought to how it works or what’s in the bottle.

“Fly repellents work by either repelling flies or killing them upon contact,” says Erika T. Machtinger, Ph.D., assistant professor of entomology at Pennsylvania State University in State College, Penn. “Repellents contain active ingredients that emit an odor or taste that flies find unpleasant and will try to avoid. Some fly repellents work by combining both repelling and killing properties. These repellents contain a combination of active ingredients that repel flies and contain insecticides that kill them upon contact.”

Active Ingredients

Most companies will list features and benefits on the front of the label, says Casey White, an entomologist and senior director of technical services and innovation for Central Life Sciences, Farnam’s research and development division.

“If it’s something that kills and repels, it’ll say ‘kills and repels’ or ‘insecticide and repellent.’ Often, it’ll call out major species of insects or arthropods, such as ticks, that the product is effective against.”

The small print is where you should pay attention to the listed ingredients, including the number and type of active ingredients and their percent concentration. The active ingredients are what give the product its killing and repelling power.

Active ingredients can be either natural or synthetic. Pyrethrins are a natural insecticide derived from the chrysanthemum flower. These offer knockdown benefits but break down quickly when exposed to sunlight. Pyrethroids are synthetic versions designed to have longer-lasting action; these include permethrin, cypermethrin, tetramethrin, and others.

Essential oils such as citronella, geraniol, eucalyptus, thyme, cedar oil, lemongrass, rosemary oil, and clove oil are natural options to repel insects. Fatty acids are another type of natural repellent, including octonoic, nonanoic, and decanoic acid.

Other ingredients include synergists, which work to amplify the active ingredients to provide greater killing power and/or longer-lasting protection. One of the most common is piperonyl butoxide (PBO). Others include butoxypolypropylene glycol and n-octyl bicycloheptene dicarboximide (MGK 264).

Comparing Products

Looking at the list of active ingredients and their percentages is one way to compare products and select the one that you think will work best for your needs.

“Formulas that use newer technology and a higher level of active ingredients cost more to make,” says Amy Cairy, vice president of marketing for W.F. Young, makers of Absorbine. For these reasons, you can expect many of the best-selling fly sprays to come with a higher price tag, she notes.

Along with comparing the levels of active ingredients, it’s also important to look at the recommended application rate, says White. A product may look like it’s half the concentration of a comparative product, but if you have to apply twice as much of it, he points out that you’re essentially applying the same amount of active ingredient—just in a more dilute form.

Fly Spray Formulation

In addition to the active ingredients, a product’s formulation is another difference to consider. Most fly sprays can be categorized as oil- or water-based, and there are pros and cons to each type.

Oil-based sprays have staying power, but can attract dirt and dust and may be irritating to horses with sensitive skin. If you see “contains petroleum distillate” on the list of ingredients, that’s the tipoff that it’s an oil-based spray.

Water-based sprays are non-irritating and less of a magnet for dust, but will likely need to be reapplied more frequently.

Many horse owners prefer all-natural formulas using essential oils and plant extracts as an alternative to chemical sprays.

Long-lasting sweat and water-resistant formulas contain ingredients that help the product stick to the hair shaft. These are designed to hold up well to rain and sweat under normal turnout and working conditions, says Cairy.

However, she notes that if you rinse your horse with a hose, sponge him off, or bathe him with shampoo, you are removing the product from the horse’s hair and should reapply the fly spray afterward.

Coat conditioners and sunscreen are other bonus ingredients you might find in a fly spray.

Choosing the Right Fly Spray

The right fly spray can depend on several factors.

“First, consider the type of flies that are prevalent in your area and choose a spray that targets those specific types of flies,” says Machtinger. “Next, consider your horse’s individual needs, such as any skin sensitivities or allergies. It’s also important to consider the spray’s effectiveness and how long it will last, and finally the ease of application and whether it requires dilution or not.”

The local climate and weather conditions, such as heat and humidity, as well as what you are doing with your horse also influence your choice of fly spray. You may want to have a few different kinds in your kit with different features and formulations. The fly spray you use right before you go in the show ring might be different than the one you’d use to turn your horse out in the field.

“For example, if you have a horse that is easily bothered by a wide variety of flies or is reactive to insect bites, you’ll want to find a long-lasting, broad-spectrum fly spray that both kills and repels insects,” says Cairy. “Or if you live where it’s hot and humid or have a horse that is prone to heavy sweating, you’ll want to reach for a fly spray that binds to the horse’s hair shaft and won’t sweat off.”

Not Enough

One of the biggest fly spray mistakes is simply user error. Either not applying enough, not using the product according to the directions, or selecting the wrong type of product for the insect species you are dealing with.

How do you know if you’re applying the recommended amount of fly spray? Cairy suggests counting sprays and measuring how many it takes to reach the recommended amount, then using that for future reference. (About 45 sprays is what she has found it takes to reach a typical 2-ounce application.)

Pest Resistance

If you find that your go-to fly spray doesn’t seem to be as effective, there may be a reason for that.

“In addition to the method of application, the effectiveness of these products can depend on the toxicity of the active ingredient to flies, and local pest resistance,” says Machtinger. “Flies can quickly develop a resistance to the active ingredients in many fly sprays (or already are resistant to them), reducing or in some cases eliminating their effectiveness.”

Pesky house flies are among the most affected by insecticide resistance. Fortunately, Machtinger reports, newer fly spray formulations using natural ingredients such as fatty acids and plant extracts have proven to be effective and longer-lasting in laboratory tests. The 2019 published study she led also suggests that formulation differences among pyrethroid products can significantly affect their efficacy.

“We do see some resistance to fly sprays, particularly permethrin,” says Cairy. “When horse owners start thinking, ‘My fly spray isn’t working the way it used to,’ we recommend that they rotate to one with a different formulation.”

When rotating products, look for something with an active ingredient that works differently than what you have been using, such as a different chemical class, advises White.

“Many of the on-animal sprays have the same mode of action, which makes incorporating other fly management tools even more important.”

Other Fly Management

There are many other things horse owners can do to help keep fly populations down, including good sanitation and manure management, and taking steps to eliminate fly breeding habitats and disrupt their life cycle.

“Scatterbaits, fly traps, feed-through larvicidal products and larvicides applied directly to fly development areas are other options that should be incorporated into a good integrated pest management (IPM) program,” says White.

It might seem like a fly is just a fly, but it’s important to try to identify what fly species you are dealing with, because they aren’t all created equal when it comes to fly control.

“To prevent flies on horses, it’s important to first understand which species of fly is the pest,” says Machtinger. “Each species will have different methods of control that are effective.”

She emphasizes the need to use a variety of tools in combination, such as good stable management and hygiene, fly masks and sheets, and species-specific fly traps.

Flies are a nuisance, but armed with the right knowledge and tools, it’s possible to fight back.

Further Reading
◆ Hoof Problems Caused by Fly Stomping
◆ Flies, Worms and Yucky Things
◆ Using Parasitoids for Fly Control
◆ Understanding Fly Spray Labels

This article about fly spray appeared in the July 2023 issue of Horse Illustrated magazine. Click here to subscribe!

The post Fly Spray 101 appeared first on Horse Illustrated Magazine.

1. Manure Management

Probably the single most important way of fly control is proper disposal of horse manure. Stable flies, the most annoying of all the biting flies that bother horses, breed in manure. Houseflies also prefer manure for reproduction.

The best way to keep these fly numbers down is to frequently remove manure from your horse’s stall or paddock. Barn aisles, turnout areas and riding arenas should also be cleaned. Clean at least once a day; more often if you can.

Once manure is scooped up, it should be taken to a manure pile far away from the barn or stored in a covered dumpster until you can remove it from your property.

Soiled bedding is another favorite spot for flies to lay their eggs. Remove wet shavings or straw from your horse’s stall every day to keep the fly population down.

2. Moisture Control

Flies love moisture and seek out wet areas to breed. Search your property for leaks from faucets, sprinklers and pipes. Look for areas where rain water gathers, too.

If your horse has a favorite spot in his stall or paddock to urinate, you can bet that flies are laying their eggs there. Put down moisture-absorbing materials to help soak up the urine. In box stalls, keep urine to a minimum with frequent cleanings and by using highly absorbent bedding.

3. Biological Controls

An eco-friendly way to combat flies is to use biological methods. Tiny parasitic wasps are widely available, and work by destroying the fly larvae before it can hatch. Signing up for a monthly delivery of these predatory insects during fly season can help keep the fly population down at your barn.

Harmless to humans and so small you can barely see them, the wasps are shipped still in the egg stage. Once a few of the wasps hatch in the plastic bag after delivery, you sprinkle the contents in and around your horse’s living area.

4. Traps

Available in a variety of different types, fly traps work by attracting flies, either through color or scent. Once the fly lands on or enters the trap, it can’t escape and eventually dies.

The simplest type of fly trap uses a sticky surface to capture flies. The flies are drawn to the color—usually orange or yellow—and land on it. The glue-covered surface sticks to their feet, keeping them from flying away. Other traps use bait to lure the fly inside. Some traps have water inside, and the flies drown because they can’t escape. Others simply trap them inside the container, where they die due to lack of food and water.

Sticky fly traps can be hung anywhere flies congregate, but should be safely out of reach of curious horses. Baited traps should be placed far from stalls since they will initially attract more flies to the area before the insects become trapped.

5. Barn Fans

Flies tend to be less active when there’s a strong breeze, as wind affects their ability to fly. So create your own wind! Barn fans hung from the ceiling over each stall and in the barn aisles can do wonders for keeping flies out of the area. Freestanding fans can also be used in barn aisles.

6. Stable Management

The environment surrounding your horses can have a big effect on the number of flies at your facility. Practicing good barn keeping will keep flies to a minimum.

Start by making sure all garbage cans are securely covered. An open trash can will draw flies from near and far. Keep feed storage containers covered as well since some grains and sweet feeds can attract flies. Clean up spilled feed right away, especially if it’s wet.

Be sure to dispose of any rotting hay on the property since this is the perfect breeding environment for flies. The combination of moisture and organic material is a haven for these pests. Also, avoid using straw as bedding since wet straw is a magnet for flies.

7. Fly Sprays

Both insecticidal sprays and repellents discourage flies from landing on your horse.

Oil-based sprays have more staying power on horses than water-based products, and both are best used in conjunction with other types of fly control. They should not be used in the vicinity of parasitoid wasps, however, since the beneficial insects are also susceptible to insecticides.

When applying fly sprays, be sure to use an adequate amount as directed on the label. If you don’t coat the horse’s hair with the spray, flies can still land and bite. For applying around the eyes, ears and muzzle, spray the product onto a washcloth and wipe it onto the horse’s face. You can also use a roll-on insecticide for these delicate areas.

8. Cover-Ups

No matter how good your fly control methods, it’s impossible to get rid of every single fly. To protect your horse from these biting pests, use cover-ups.

Fly masks are the most effective way to protect your horse from flies. Face flies are notorious for feeding on the mucus in your horse’s eyes, causing irritation and potentially spreading disease. You can also use a mask with attached ear covers to keep biting gnats out of his ears.

A fly sheet prevents flies from landing directly on your horse’s body. The lightweight mesh blanket protects your horse’s chest, back, sides and hindquarters from biting flies. Add mesh leg wraps to protect the lower legs, and flies will have a hard time finding a place to bite your horse.

By using these methods, you can make a big impact on the number of flies that live on your property and pester your horses.

9. Spray Systems

In a barn environment, an overhead fly spray system can be effective at keeping fly populations down. Spray systems release a repellent or insecticidal mist periodically throughout the day. The spray comes down onto the horses and prevents flies from landing and biting. The system can be designed to spray directly into both stalls and barn aisles.

After installing a spray system in your barn, choose the type of insecticide or repellent you want to use. If you are concerned about introducing chemical fly products into the environment, opt for natural formulations.

10. Supplements

Supplements designed to prevent flies from breeding in manure or to discourage flies from biting are another option for your horse. Insect growth regulators (IGR) are chemicals that disrupt the fly’s ability to reproduce by affecting the pupa stage in the life cycle. When the active ingredient in the IGR is present in the horse’s manure, the fly larvae can’t develop to adulthood.

A feed-through product containing an IGR is added daily to the horse’s food, and then passes through the horse and is deposited with the manure. The IGR has no effect on the horse, but wreaks havoc on the fly population.

Natural supplement formulas containing garlic, apple cider, yeast and other ingredients with natural fly-repelling properties are reported to discourage flies from biting. These products must be fed daily to be effective.

Further Reading on Fly Control for Horses and Barns

◆ Natural Insect Repellents for Horses
◆ Flies, Worms and Yucky Things

This article about fly control for horses and barns appeared in the July 2015 issue of Horse Illustrated magazine. Click here to subscribe!

The post 10 Ways to Banish Flies from the Barn appeared first on Horse Illustrated Magazine.