The first step in controlling flies is getting fresh manure away from the barn. Resort to sprays to protect your horse from the biting pests. There are many fly control products on the market, from sprays and wipes to nematodes that devour fly larvae before they hatch. Each product or method controls some flies better than others. Try out several to determine what works best for you.
Small biting flies of different varieties really like to get along the horse's belly midline, in the ears, right at the top of the foretop, and in other places the horse can't reach with his built-in fly swatter, the tail. Spraying the horse every morning before turnout helps relieve some of the misery, but not all. Use fly spray especially before you saddle up and ride. This will prevent your horse from getting distracted by the biting bugs and possibly even bucking you off in a desperate effort to remove a fly from his butt.
During fly season, spray the legs before you start grooming and tacking up to prevent an accidental kick. Horses sometimes try to shake off a fly by shaking a leg, and if you happen to be in the way, you could get kicked unintentionally. Read the product label and follow the instructions on the bottle for how much and how often to spray your horse. Keep an eye on the horse for an allergic reaction, usually in the form of hives. Some products that didn't bother a horse last year may cause hives this year, so don't be complacent just because you use the same fly spray every year.
Never spray fly spray on the horse's face. Spray it on a mitt or a small brush reserved exclusively for this purpose and carefully apply it to the horse's face, avoiding her eyes. You could also use a roll-in pesticide for the face and around the eyes.
When the flies are really bad, put a fly mask on the horse to protect the eyes from the biting swarms that like to settle in the corners. These are made of a mesh material that allows the horse to see out but keeps flies from getting in.
You can also buy mesh fly sheets that cover the horse's body but are light and not hot in warm weather. Another tactic is to put your horse in his stall during the times of day when the flies are out in force — typically midday to dark — and turn him out overnight when the flies are not as bad.