Around our barn, I use a mixture of citronella oil, skin-so-soft, cider vinegar, and permethrin, it works really well, one ounce each of the oil, skin-so-soft and permethrin, then fill the rest up with cider vinegar, I mix it in an old gallon vinegar bottle, then put it in sprayers, make sure you shake well. Your horse will kinda smell like a salad, but it's way better than the flies and mosquitoes!

TY for the tip I'll have to try that

your welcome JF Horses and good luck :D