Durvet Permethrin-10 Long-Lasting Fly Repellent with up to 28 days of residual activity for just pennies a horse! This long-lasting fly spray features a new, exclusive, safer formula. (Residual activity for up to 28 days*) Our best results came from mixing from 2 to 4 ounces of concentrate in a gallon of water and for some extreme infestations up to 6 ounces per gallon for spot treatments on the ears, face, and along the backline. ( Mfg suggests starting at 2 ounces per gallon and increasing the amount if needed in heavy infestations.) Special, non-burning formula contains no solvents or petroleum distillates. It has virtually no odor when mixed with water. Effective against one of the widest range of insects available. Among the many pests this fly spray is effective against are: horn flies, face flies, lice, ticks, deer ticks, mosquitoes, and many other pesky insects.