The bug invasion may still be weeks away, but you can start now to retrain horses who react violently to the noise or sensation of being sprayed with fly spray. They may spin, back up or even rear to escape the hissing mist, and their reaction can be worsened by a threatening posture or actions of a handler who's determined to make them stand still. Here are some steps for breaking the self-perpetuating cycle of sprayer terror.
Use a good-quality, quiet sprayer. Pump sprayers that must be "primed" first, like a beer keg, produce their mist in near silence.
Control your body language. Rushing toward a horse's head with sprayer extended is a sure to look threatening. Retrain yourself to use controlled, relaxed mannerisms. Approach the horse at his shoulder, use the spray bottle in slow, rhythmic sweeps, and respect the horse's "threat" zones (head and hindquarters).
Acclimatize the horse to the noise. Fill the sprayer with water and stand outside your horse's stall while he eats. Spray at regular intervals, pointing away from the horse, until he ignores the noise in favor of food. Then repeat the process inside the stall, again without actually spraying the horse. A few sessions of dinnertime spraying should reduce his terror. In fact, association with food may even make spray sounds welcome.
Desensitize the horse to the spray. Once noise is no longer a problem, find the level of spray contact your horse will tolerate. Start with gentle mist, still using plain water. Pull the "trigger" slowly, and aim the spray at the shoulder. If even this sensation is intolerable for your supersensitive horse, you can flick water gently at him with your fingers first. When he accepts this, reintroduce the light spray. Continue at base comfort level until he ignores the misting and then increase the pressure of the spray.
Move to other areas of the body as your horse accepts spraying at each site and intensity. Whenever he objects, return to the previously acceptable level until he settles, and then try again.