Permethrin is what kills fire-ants. I buy from the co-op "Hi-Yield 38 Plus" termite control concentrate with 38% permethrin. Garden
Supply Centers typically sell a 25% concentrate. One ounce of concentrate per gallon is plenty strong enough to kill fire-ants. I've killed them
with 1/2 ounce per gallon. I've used a pump-up sprayer and an agricultural sprayer on the back of a tractor but mostly I just mix it in a 2-1/2 gallon
plastic Round-Up jug. 2 ounces of concentrate in the jug filled with water is enough. I carry one on the riding mower when I mow the grass.
To kill a fire ant hill, the queen has to be killed. If it's a single mound, then in the center of the mound will be the tunnel that goes straight down into
the nest. In a large hill, the queen might be three feet down in the ground. Using a pump-up sprayer, spray the top of the mound to keep them from wandering over to your feet, then poke the wand around in the center of mound until you find the hole going down. For large mounds inject a much as a pint. If you use the jug, just pour a little around on the center of the hill until you can see where it starts going into the ground.Then pour about a pint into the hole. They will be dead in five minutes. Some nests don't have a central mound but are spread out over an area maybe four feet in diameter with no central mound. These are multiple queen nests and each hole must be located and poisoned. These may require multiple applications to get all the queens. Good Luck! Persistence is the key.