Beef up your fly-defense arsenal to keep these annoying adversaries from breeching your barn’s front lines.
The sweet stirrings of summer are already abounding and while I welcome the warmer weather, extra daylight, and colorful blooms, I also realize this means an army of flies is preparing its annual attack on my gelding and his barn-mates. As “Rio”—the sweet 19-year-old Thoroughbred I’m leasing—gets on in age, I grow increasingly concerned about the stress and potential health risks these menaces bring each year.
Flies are indeed annoying pests that bite, buzz, and pester our horses, but they’re also harbingers of disease such as salmonella, vesicular stomatitis, pigeon fever, equine infectious anemia, and influenza. These odious insects can trigger allergies, dermatitis, and eye ailments like conjunctivitis, and constant stomping can contribute to arthritis, ring bone, other impact-related injuries, and even weight loss.
Flies are an unfortunate—yet inherent—aspect of managing horses, and you’re not going to be able to take down every single little buzzing vermin. The good news, however, is there a number of effective management strategies and munitions you can employ to put these loathsome troops into retreat. We manage about 40 horses and a merry band of mini-donkeys at my barn—all with unique sensitivities to flies; here are some of the smart strategies we use to reinforce our fly resistance.
First Lines of Defense
Before summoning the heavy artillery, it’s crucial to implement savvy barn-management tactics to make your facility least hospital to flies.
Manage Or Remove Manure: Manure is the housefly’s meal of choice and the more manure around your barn, the more flies you’ll have to battle. Reduce flies’ access to manure buffets by regularly cleaning stalls, pens, and other areas of confinement; if possible, remove manure to an off-site location once a week or cover with a heavy tarp and treat on-site for later removal.
Control Moisture: 
Air Power: For stalled horses, large fans can deliver hefty blasts of air to knock flies off their targets; for horses kept on pasture, make sure to provide access to open, breezy spaces.
Keep Foodstuff Under Wraps: Properly dispose of all garbage and keep grain, supplements, and other feeds sealed under air-tight lids.
Avoid Fly-Magnet Neighbors: If possible don’t pasture horses near cattle or other livestock; cow manure, in particular, is a delicacy for vicious horn and face flies.
Anti-Fly Arsenal
Topicals
How They Work: Sprays, roll-ons, wipes, and gels serve as a contact repellent, meaning they provide a vapor barrier to fend off flies. Topicals contain natural (pyrethrums) and synthetic insecticides to knock down or deter flies on contact. There are also insecticide-free products that use citronella, essential oils, certain fatty acids, and other plant-based ingredients to confuse and overwhelm flies’ sense of direction, so they’re less likely to feast on your horse.
Pros & Cons: Topicals are easy to apply and convenient for on-the-road use when showing or trail riding, but the protection they provide is relatively short-lived and largely depends on the product. Prices vary depending on ingredients and method of application; generally, the lower the cost, the shorter the protection duration. While there are a number of products with sweat-resistant properties, if your horse sweats significantly or is bathed often, topicals will be less effective and may have to be applied more often.
Traps
How They Work: Using some variation of fly bait or attractant, traps lure flies onto a sticky surface or into a receptacle where the insects become entrapped and die. Traps help manage adult flies that have evaded other control measures without putting insecticides into the air.
Pros & Cons: Traps are generally inexpensive and are useful regardless of other fly-control measures because of their ability to manage adult flies. Most traps, however, only attract house and blow flies, so they may not be effective if you’re battling other species.
Feed-Through
How they work: Also known as insect growth regulators, feed-throughs contain ingredients that pass through the horse’s system into manure to prevent larvae and pupa from developing and hatching. Feed-throughs are typically administered with a horse’s grain ration from early spring to late fall and work best when used in conjunction with fly traps and topicals.
Pros & Cons: Feed-throughs are safe, easy to use, and relatively inexpensive, but they don’t impact adult flies. They also kill some beneficial microorganisms, and they’re ineffective if not administered in the correct dosage to all horses at your facility.
Supplements
How they work: Specifically formulated with ingredients that deter flies and other biting insects from feasting on your horse, supplements can also play a role in helping combat fly populations.
Pros & Cons: Chemical- and insecticide-free, supplements are an effective fly-control tactic at my barn whether we’re feeding to one horse or many, and they’re easy to dole out with our horses’ daily grain rations. It can take up to a month for nutrients to build up in a horse’s system, so we start feeding insect-control supplements well before fly season is in full swing.
Fly Parasites
How they work: Released near manure piles and other common fly-breeding sites, these tiny, low-flying wasps use the fly pupa as a host to kill developing flies before they hatch, which prevents new generations from maturing. Parasites emerge as active wasps in about five days; it can, however, take up to 30 days for noticeable results, as parasites don’t impact flies that have already hatched. Parasites work best if released before flies become rampant; once they’re in circulation, you’ll only need to release new parasites every three to four weeks, depending on your fly population.
Pros & Cons: Parasites are safe, low-maintenance, chemical-free, and don’t bite or sting people, horses, or pets, but they don’t affect water-breeding flies like horse and deer flies. If your neighbor doesn’t have a good fly-control program, flies can still migrate to your facility. Parasites work best in more condensed facilities and are cost effective in almost all set-ups.
Barriers
How they work: Fly sheets, masks, and boots provide external protection from flies and other biting insects. Made out of lightweight mesh fabric, fly sheets protect horses from withers to rump and many also offer neck, chest, and belly protection. Fly mask designs vary, but they generally protect crucial facial areas; some masks only cover a horse’s eyes and others extend over the ears and down the muzzle. Fly boots—also typically made out of a lightweight mesh—protect sensitive skin on the lower legs. Barrier fly protection is a great option for horses living in close proximity to cattle or other livestock that attract horn and face flies or when boarded at a facility without a broad-spectrum fly-control program.
Pros & Cons: Manufacturers have created some incredibly innovative mesh fabrics that are super lightweight and breathable to prevent horses from overheating. Many of these mesh fabrics also have built-in sun protection, which is especially beneficial for horses with exposed pink skin; sheets can also protect against sun-bleaching. Masks can help prevent conjunctivitis caused by nagging flies and stave off other allergies; fly boots can reduce stomping and allow horses to graze more peacefully.
Courtesy of SmartPak