6 Best Horse Fly Concentrates For Pasture Spraying Old Farmers Swear By

There’s nothing that ruins a peaceful summer evening on the farm faster than the buzz and bite of horse flies. You see your horses tail-swishing, stomping, and running from a pest you can barely see. For a small operation, keeping your animals comfortable and safe from these aggressive insects is a top priority, and that’s where a good pasture spray system comes in.

Disclosure: As an Amazon Associate, this site earns from qualifying purchases. Thank you!

Understanding Pyrethrin vs. Permethrin Sprays

When you start looking at fly control concentrates, you’ll see two names pop up constantly: pyrethrin and permethrin. It’s crucial to know the difference because they do very different jobs. Think of it like using a tack hammer versus a sledgehammer.

Pyrethrin is the tack hammer. It’s a natural insecticide derived from chrysanthemum flowers. Its biggest advantage is a rapid "knockdown" effect—it stuns or kills insects on contact almost instantly. The downside? It breaks down very quickly in sunlight, offering almost no lasting protection.

Permethrin is the sledgehammer. It’s a synthetic version designed to mimic pyrethrin’s properties but with one huge improvement: stability. It doesn’t degrade quickly in the sun, so it provides residual control, continuing to kill or repel insects for days or even weeks after application. For pasture and premise spraying, this lasting power is exactly what you need.

Many of the best formulas actually combine both. They use pyrethrins for the immediate relief of a quick knockdown and permethrin for the long-term residual barrier. They also often include a "synergist" like piperonyl butoxide (PBO), which prevents an insect’s metabolism from breaking down the insecticide, making both ingredients more effective.

Gordon’s Permethrin 10 for Broad-Spectrum Control

Gordon’s Permethrin 10 is a classic for a reason. It’s a straightforward, no-frills concentrate that gets the job done without a lot of fuss. This is the kind of product you’ll find in the sheds of farmers who value reliability over fancy marketing.

Its main strength is its versatility. The 10% permethrin formulation is effective against a huge range of pests beyond just horse flies—think ticks, mosquitoes, spiders, and gnats. You can use it in a pasture fogger, a high-pressure sprayer for the barn exterior, or even as a premise spray inside stalls (with animals removed, of course). This multi-use capability is a huge plus on a hobby farm where you want one product to solve several problems.

Be aware that it’s an oil-based concentrate. This helps it adhere to surfaces and foliage for better residual action, but it means you need to agitate it well when mixing. It also might not be ideal for certain types of automated misting systems that work best with water-based solutions.

Pyranha 1-10 PX: A Reliable Water-Based Formula

If you run an automatic misting system in your barn or a fine-mist fogger for your pasture, Pyranha is a name you’ll hear a lot. The 1-10 PX formula is specifically designed for these systems. It’s a water-based concentrate, which makes it easier to mix and less likely to clog fine nozzles.

This product is a great example of a combination formula. It contains both pyrethrins for quick knockdown and permethrin for residual control, plus a synergist to boost their power. When your system kicks on, it immediately drops the flies in the air while also laying down a protective barrier that keeps working after the mist settles.

The tradeoff for the convenience of a water-based formula is that it may not have the same weather-resistant longevity as a heavy oil-based product. However, for systems that spray on a regular, automated schedule, this is less of a concern. It provides consistent, reliable control day after day.

Durvet Permethrin 10% for Multi-Species Pastures

For the hobby farmer with a mixed bag of animals, Durvet’s Permethrin 10% is an economic powerhouse. The real value here isn’t just its effectiveness, but its broad labeling. Many farmers trust it because it’s often approved for use on or around multiple species, including horses, cattle, goats, and poultry.

This is a huge advantage. Instead of buying separate fly control for the horse pasture, the chicken coop, and the cattle run, you can use one jug for everything. It simplifies your inventory and reduces costs. You can mix a batch for your pasture fogger and then use the same concentrate (at a different dilution) to treat the poultry house for mites.

Like Gordon’s, it’s a workhorse 10% permethrin solution. It provides solid residual control against a wide spectrum of insects. Always read the label for specific dilution rates and application methods for each animal, as they can vary significantly.

Absorbine UltraShield EX for Long-Lasting Action

Absorbine is a premium brand, and their UltraShield EX is the top-of-the-line option for those who want the longest possible protection. While famous as a ready-to-use spray, the concentrate offers the same powerful formula for large-area application. It’s more expensive upfront, but the goal is to spray less often.

The formula is complex and effective, containing permethrin, pyrethrin, and PBO. What sets it apart is the addition of sunscreens and coat conditioners. While the conditioners are more relevant for on-animal application, the sunscreens help protect the active ingredients from UV degradation, extending their lifespan and effectiveness in an open pasture.

This is your choice if your main limitation is time. If you can only get out to spray the pasture once every week or two, the extended duration of UltraShield EX can be worth the extra cost. It’s a "set it and forget it" approach for busy farmers.

Farnam Repel-X pe: A Time-Tested Fly Concentrate

Farnam is one of the oldest and most trusted names in horse care. Repel-X has been around for decades, and its formulation has been tweaked over the years. The "pe" version is a concentrate that relies heavily on pyrethrins and PBO for its punch.

Unlike the permethrin-dominant products, Repel-X pe is geared more toward rapid knockdown. It’s fantastic for clearing an area quickly. If you need to fog a paddock an hour before turning horses out, this is a great choice. It will knock down the active flies and make the space comfortable right away.

The downside is its short residual life. Because it’s pyrethrin-based, it won’t give you the multi-day protection of a permethrin spray. This makes it less ideal as a primary pasture-wide solution unless you plan to spray frequently. It’s a specialized tool, not an all-purpose barrier.

Martin’s Permethrin 10% for Large Area Coverage

Martin’s Permethrin 10% is another rock-solid, cost-effective choice that functions much like the offerings from Gordon’s and Durvet. In many rural areas, the "best" brand often comes down to what your local co-op or feed store carries, and Martin’s is a common and reliable sight on those shelves.

Its primary advantage is often price, especially when buying in larger quantities. For a hobby farmer with several acres of pasture to treat, the savings can add up over a season. The 10% permethrin formula is proven and provides excellent residual control for horse flies, deer flies, and mosquitoes that make pastures miserable.

Don’t overthink the choice between Martin’s, Durvet, and Gordon’s. They are all highly effective 10% permethrin concentrates. Your decision will likely be based on local availability and which one offers the best value per gallon at the time of purchase.

Safe Application Tips for Pasture Fogging Systems

Having the right concentrate is only half the battle; applying it safely and effectively is what really matters. A powerful tool used improperly can cause more harm than good. The goal is targeted pest control, not environmental contamination.

First and foremost, read the entire label before you even open the bottle. It contains critical information on mixing ratios, approved application sites, and personal protective equipment (PPE). These aren’t suggestions; they’re requirements for safe and legal use. Ignoring them is irresponsible.

When you’re ready to spray, timing is everything. Apply in the very early morning or late evening when the wind is calm. This ensures the fog or mist settles on your pasture, not your neighbor’s garden. It’s also when beneficial pollinators like bees are least active. Keep animals out of the pasture during application and respect the re-entry time specified on the label. Finally, be acutely aware of any ponds, creeks, or wells on your property—most of these concentrates are highly toxic to aquatic life, and you must prevent any drift or runoff from reaching water sources.

Ultimately, the best horse fly concentrate is the one that fits your specific situation—your budget, your animals, and the amount of time you have. Start with the product that best matches your needs, apply it safely, and watch your horses enjoy a more peaceful pasture.