Best thing I have found for controlling fire ants is a product called Taurus. Can be bought at probably any farm chemical supply. Only mix 4 oz. with enough water to spray an acre. it is a repellant. Doesn't kill them but they will definitely move away from any area that has been sprayed. I tried everything to get rid of them in my yard. This is the only thing that has worked for me. Only have to spray once a year.