Everywhere in the world, at some time of the year a horse owner's attention turns to the subject of pest control. If you have horses, you have flies, along with mosquitoes, gnats and all manner of other flying irritants.

There are probably as many fly-control approaches as there are different barns in various regional climates, and creating a successful abatement program requires a thoughtful multi-layer approach. We all want to keep our horses healthy, happy and safe – preferably without spending a small fortune. But how?

Manure management is a challenge for barns of any size, but essential to reducing the number of flies.  

Let's assume you've already done all the basics – picking up manure in pens and stalls at least daily, eliminating standing water, emptying garbage cans, etc. For the next layer of management do you rely only on spray-on fly repellent or do you go one step farther with a feed-through product. What about a facility-wide approach such as a barnwide sprayer system?

All those options rely on chemical pesticides of some type and they all require considerable financial outlay. Just do the rough math to total the cost of all the fly spray you've used in your horse-owning lifetime. There's a cost we'd all like to do without.

I've written before about chemical fly sprays, all those increasingly pricey spray bottles of liquid most horse owners douse their horses in without a thought – or without reading the labels, many of which have pretty startling warnings. So, on that subject, read the other article and please read the label on your spray of choice.

Another type of chemical abatement comes in the form of feed-through products, which were coming on the market when I was starting my professional life in the horse business and which were greeted by many barn managers as a miracle product. The training barn where I started my career used Equitrol, one of the first feed-throughs available to horse owners. It contained an organophosphate that was supposed to pass through the horse with no effects and end up in the manure, where it would interfere with the nervous systems of the fly larvae. A 2004 lawsuit showed that at least some horses absorbed enough of the chemical to cause harm, despite the company's product labeling asserting safety.

Solitude 1/2 oz.
48 cents#
Simplifly 1 oz.
36 cents
Equitrol II 1 oz.
29 cents
$ 8.82
*Daily recommended dose for a 1000-pound horse
#Prices taken from major catalog and online equine-product retailers.

My best consumer advice: don't rely on the company profiting from selling the product to tell you it's safe for your horse. Just because a product is touted by the marketing department of a well-known corporation (in the case of Equitrol it was Farnam), don't assume it “must be okay.” Do some research to find out what the chemicals are and what potential dangers they might pose.

That starts with reading non-marketing part of the label – the back where the “active ingredients” are listed. For example, currently marketed feed-through products include Simplifly and Equitrol II, which contain diflubenzuron, and Solitude with cyromazine.


Standing water in drinking and bathing areas attracts flies and provides breeding ground for other pests. . Hint: if the water has a green cast from algae growth, it has been there too long.


Even if I were happy about feeding my horse a daily dose of a chemical, with multiple horses I would find these products to be quite expensive. (See table above)

Choosing the best fly-control approach is especially challenging for those of us who prefer to minimize the use of chemicals that can irritate us and our horses and have a detrimental effect on our environment and the plants and animals around us.

One of the most tempting non-chemical feed “supplement” options involves feeding horses diatomaceous earth (DE), a fine powder made from the fossilized silica remains of diatoms, a type of hard-shelled algae. This product meets my two favorite criteria: it's not a harmful chemical and it's inexpensive. Though online sources show prices as high as $60 for a 50-pound bag of food-grade DE, at least one feed store in my area sells that size for $24.99.

But, if you want to see a whole lot of mostly unsubstantiated health claims, just point your web browser in the direction of DE. Among the claims that make this product – also labeled as “fossil shell flour” – sound like a cure-all, you'll find plenty of sites touting its use for barn pest control. Uses include topical application around the stable to kill flies and other pests as well as feeding it to horses as a dewormer or feed-through fly control.

Not much research seems to exist showing the efficacy of the internal uses for horses, though there seem to have been some favorable results in other species, namely dairy and feeder cattle. And there are concerns about feeding DE to horses who might have digestive issues, such as ulcers.

I also know of an instance when a cribber was fed DE and ended up causing significant wear to his teeth, likely because some of the abrasive powder stayed in his mouth and effectively ground down his upper front teeth when he rubbed them back and forth on the bars of his pen to find the perfect hold for sucking air.

Food-grade DE (1/2 cup)
12.5 cents
Bug Off Garlic*
25 cents
Generic Garlic (.5oz)
17 cents
*Lowest daily recommended dose for a 1000-pound horse.

Another feed-based option is garlic, which is more expensive than DE (with which it is mixed in some products) but cheaper than the chemical feed-throughs. Garlic – in the form of granules of powder – has the advantage of being readily available and palatable to most horses. There are a number of garlic-based products marketed especially for horses, some of which have other ingredients in the mix, or you could simply purchase generic garlic granules from your bulk herb seller. I do the latter, purchasing from whichever of my herb resources has the best price, but I've also used the product sold by Springtime Products and can attest to its quality.

Aside from widespread anecdotal evidence, there doesn't seem to be any research regarding the effectiveness of this option. One oft-quoted safety-oriented study from 2005 concluded that feeding horses garlic caused anemia, so if your horse is prone to that condition you might want to think twice and, of course, have a conversation with your veterinarian. I will note that at the study dosage, you'd be feeding a 1,000-pound horse about a cup (8 oz.) of garlic per day. That's way more than any of the products I've seen or used suggest; in fact, it's a ridiculous amount and I'm surprised the horses would eat that much. In contrast, I have confidently fed at a rate of less than ½ ounce per day for four to six months of the year with good results.

For both effectiveness and safety – for your horses and your world – I believe using beneficial insects known as fly predators really wins out. Nothing for the horse to ingest. No chemicals. And it's so cost-effective, especially for larger operations such as boarding barns. That fact may be surprising to some barn owners/managers, as I've heard from several sources over the past couple of years that they don't use the predators “because they're expensive.” Compared to other fly management options, that's clearly not true, as the table below shows using actual prices from the two major suppliers, both of which sell online via very informative websites. You'll see that for a small operation, the predators might seem pricey (though still cheaper than feed-through chemicals.) But given the economies of scale, for boarding facilities they're dead cheap. The only less expensive option would be to do nothing.

Arbico (2 horses)
Spalding (2 horses)
Arbico (40 horses)
Spalding 40 horses
*Using the smallest number of units recommended

The other piece of misinformation I've come across locally regarding fly predators was had to do with the wasps' suitability to our hot, dry climate. After encountering one local barn owner's assertion that the predators only thrive in cool, damp regions, I contacted Arbico, which just happens to be located right here in Tucson. The very helpful consultant assured me that because the company's wasps are raised at their local facility, they're perfectly adapted for use by Arizona horse owners.

While I was commiserating with the Arbico employee about why more horse owners and barn managers don't use this environmentally friendly and effective approach to fly control, she shared a piece of information that frankly amazed me. She said in her experience a significant percentage of customers who cancel their fly predator programs say they're doing so because “it's too much trouble.”

Now that really surprised me. I've been reading the various companies' literature about how to use the predators effectively and it just didn't seem that difficult. Watch Spalding Labs' excellent video (below) and see if you think sprinkling wasps around your property sounds complicated or time-consuming.

I haven't owned or managed a property since I learned about fly predators, so I have never been the person in charge of deploying them. But I contacted someone who has used them for years to get an informed perspective and she verified my impression, confirming that the predators could be correctly released on a 10-acre, 40-horse property in about 15 minutes. I have witnessed the effectiveness of this fly-control option on properties of all sizes – with as few as two horses up to as many as 40 – and for me it's a no-brainer.


My ideal choice? Combine a monthly application of the beneficial insects with spot use of any of the readily available fly traps. Feed a garlic-based supplement during peak fly months, maybe with an added dose of apple-cider vinegar. And, as needed, use a non-insecticidal repellent spray to give your horse added relief from pests without killing the fly predators.

That's precisely the set-up my retired gelding, Ichobod, enjoys at his retirement abode. The property owner uses fly predators and hangs fly traps to draw flies away from the areas where the horses eat and hang out. I supply the garlic and cider vinegar. And, though we had a weirdly wet spring and are in the bug-infested monsoon season, I've only noticed Ich being bothered by flies and felt the need to spray him with my homemade repellent a handful of times. Effective and inexpensive – the best of all worlds.



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