Manna Pro Opti-Force Sweat Resistant Fly Spray for Horses 32 oz.Manna Pro Opti Force Fly Spray Sweat and weather resistant fly spray that lasts up to 14 days. It provides repellency and quick knockdown from biting and nuisance flies, gnats and mosquitoes (Culex spp.) that may transmit West Nile Virus. For use on horse and ponies. Key Bullet Points: For use on horses and ponies Sweat Resistant 14 Day weather resistant Protection Last long without causing skin irritation EPA Reg. No. 53883 150 84151 EPA Est. No.