I hate chemicals, won't let them near my home. I have used Poultry protector to spray out the coops and roosts maybe there is something like that for horses. Also the ff is suppose to keep flies down so we'll see on that one. and I bought those fly traps [recycled bottles] that have the attractant you mix with water, they are kinda stinky but work real good. can't hang them inside though.I am super sensitive to scents, no perfume etc... and i bet it was! we had a heck of a time getting that poor swallow off of it, a big farm strip type. So still trying to sort alternatives there don't like spraying the horses with chemicals.