• Mix concentrates correctly. If you’ve purchased a concentrated fly control product that needs to be mixed with water, read and follow the directions closely. Trying to “eyeball” or guesstimate how much product to use can leave your horse unprotected.
• Shake the product before applying. A vigorous shake of the bottle before you spray will ensure the product is remixed thoroughly.
• Groom before applying fly spray. If you are spraying fly spray onto caked mud and dirt, all you are doing is protecting mud and dirt. As that debris falls away, so will the product. Take a moment to brush your horse before you spray. He doesn’t have to be show-ring ready, but make sure the worst of the dirt is gone.
• Apply enough product to enough places. A few casual spritzes of fly spray over your horse’s topline isn’t going to do much to keep bugs away. Most manufacturers recommend apply 2 to 3 ounces of product, which can be as much as 40 sprays of the bottle. Apply the product everywhere—especially down the legs and under the belly where flies congregate. Use a lotion of roll-on product on the face and ears, or spray the product onto a rag and gently wipe those areas.
• Re-spray if the horse becomes soaked. A steady rain or after-workout hosing will wash most fly sprays away. Reapply product if your horse’s coat becomes soaked through either of these says. Some fly-spray formulations are designed to be sweat-resistant, but others are not and may be washed away in sweat just as they would with water—so check the label to determine if you should reapply a specific product after a sweaty riding session.

Before trying any fly spray on a horse, be sure to test it on one small area of the horse and wait 24 hours to see if there is a reaction.