How to Beat Flies on Horses: Feed-Through, Fly Spray, and Physical Barriers

How to Beat Flies on Horses: Feed-Through, Fly Spray, and Physical Barriers
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Three Layers of Fly Protection That Work Together

No single product eliminates flies completely. The horse owners who manage fly pressure most effectively do it with a layered approach, one that addresses flies at the larval stage before they emerge, repels and kills adult flies on the animal, and provides a physical barrier in the areas where spray coverage is limited.

Getting those three layers working together before fly season peaks makes the season measurably more comfortable for horses and significantly less frustrating to manage.

Layer 1: Stop Flies Before They Start with Feed-Through Fly Control

The most efficient way to reduce fly populations around the barn is to interrupt the life cycle before adult flies ever emerge. Feed-through fly control products contain an insect growth regulator (IGR) that passes through the horse's digestive system into the manure, where it prevents fly larvae from completing development into adults.

SimpliFly Feed-Thru Fly Control with LarvaStop is one of the most trusted and widely used feed-through products available for horses. Its LarvaStop IGR prevents the formation of the fly larvae's exoskeleton during molting, breaking the reproductive cycle of house flies and stable flies at the source. It is highly palatable, contains no organophosphates, and fits easily into an integrated pest management program.

Two practices determine how well feed-through fly control performs:

Start before fly season begins. The IGR needs to be present in the manure before the first flies of the season emerge. In the Mid-Atlantic region, starting by March 1st is recommended to ensure coverage from the beginning of fly activity through the season.

Treat every horse on the property. Untreated horses continue to contribute to fly larval development regardless of what treated horses are receiving. For maximum reduction in adult fly populations, all horses in the barn and on the property should be on the program consistently.

For a broader comparison of feed-through options including Altosid IGR and ClariFly, The Mill's guide to controlling flies with feed-through additives covers product selection based on management situation and housing type.

Layer 2: Spray the Flies Away

Feed-through products manage larval populations in manure. On-animal fly sprays address the adult flies that are already present and actively landing on horses. Choosing the right spray for the situation requires understanding the chemistry behind the active ingredients, since different formulations offer different durations of effectiveness, levels of water and sweat resistance, and suitability for sensitive skin or foals.

Pyrethrins: Plant-Based, Fast-Acting, Daily Protection

Pyrethrins are organic compounds derived from chrysanthemum flowers. They act on the nervous systems of insects and are biodegradable, which means they break down rapidly with sunlight exposure. Most pyrethrin-based sprays include synergists such as piperonyl butoxide to protect the active ingredient from UV degradation and extend effectiveness. These products are well suited for daily application situations where a natural-origin formula is preferred.

Products in this category available at The Mill include:

Permethrin: Synthetic Protection, Water-Based Options

Permethrins are synthetic forms of pyrethrins formulated to control a broader range of external parasites including ticks, lice, gnats, and multiple fly species. Water-based permethrin sprays are suitable for daily use and can also be applied to premises including stalls, barn aisles, and fencing as a surface spray. An important safety note: permethrin is toxic to cats, birds, fish, and beneficial insects including honeybees. It should not be applied in areas where cats are present, and any runoff from premise applications should be managed carefully.

Products in this category available at The Mill include:

Pyrethroids: Oil-Based, Long-Lasting, Sweat-Resistant

Pyrethroids are synthetic forms of pyrethrins that resist UV breakdown far better than natural pyrethrins, making them effective for several days after application rather than requiring daily reapplication. Oil-based pyrethroid formulas bind to the hair shaft and maintain effectiveness through sweat and light rain, which makes them the better choice for horses in hard work, turnout, or show situations where daily reapplication is not practical.

Products in this category available at The Mill include:

  • Absorbine UltraShield EX Fly Spray - kills and repels over 70 species of flies, ticks, mosquitoes, and gnats; weatherproof and sweat-resistant with up to 17 days of protection; contains aloe, lanolin, and sunscreens as coat conditioners

  • Farnam Endure Sweat-Resistant Fly Spray - RepeLock conditioner technology binds to the hair shaft for lasting protection through sweat and moisture; effective up to 14 days per application

  • Pyranha Wipe N' Spray - pyrethrum-based, citronella-scented formula that can be sprayed or wiped on; leaves a high shine and is a consistent favorite among show horse owners

  • Tri-Tec 14 Fly Repellent - protects against six types of flies plus gnats, mosquitoes, lice, and deer ticks; designed for multi-day protection in a single application

Layer 3: Physical Barriers - Cover Up Your Horse

The face and lower legs are the areas flies target most aggressively, and they are also the areas where spray application is most limited. Physical barriers fill that gap and provide protection that sprays cannot fully deliver.

Fly Masks protect the eyes, face, and ears from face flies and gnats, which are responsible for spreading pinkeye and causing the irritation that drives horses to rub their faces on structures. Fly masks are available in styles with and without ear coverage and with or without extended nose pieces, allowing selection based on the horse's specific sensitivity and management situation.

Fly Sheets cover the body and are particularly valuable for horses with sensitive skin, horses that react strongly to insect bites, or horses in turnout situations where spray reapplication is not practical on a daily basis. Many fly sheets also provide UV protection, making them useful for horses prone to sunburn or coat bleaching.

Fly Boots protect the lower legs from stable fly biting, which is one of the primary causes of the leg stomping and restless behavior that disrupts grazing and turnout. Lightweight and easy to apply, fly boots are a practical addition for horses that stomp persistently despite other fly control measures.

Browse The Mill's selection of fly masks, sheets, boots, and related physical barrier products in the Horse Health and Stable Supplies collection.

Building a Complete Summer Fly Program

The programs that deliver the best results through a full season combine all three layers: a feed-through IGR started before fly season to reduce larval development, a fly spray matched to the horse's workload and application frequency needs, and physical barriers that protect the face and legs where spray coverage is insufficient.

For more detail on barn-level fly management including manure management, fly traps, predators, and ventilation strategies, The Mill's complete barn fly control guide covers the full environmental approach alongside on-animal control.

Visit any local The Mill store or browse the full Horse Health collection at The Mill | Your Store for Pet, Lawn, Garden, Farm, Bird, and Deer to find the right combination of products for the barn.

Fly Control Products Available at The Mill

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