How big is the nest? I find smaller ones in my horses yard, and I've found that fly spray (I use Flysect) also kills ants. I pour some of the Flysect down the hole, and that seems to really take care of the problem!
I'm fighting them in a stall now too, only I haven't found a mound there just an ant "superhighway" where they come in and out all day. I've put the granulated fire ant killer in the area I found them, and moved my gelding out to another stall for a day or so.
I've been using Hosscrazy's idea. Been pouring the spray on insect repellent/killer that we use on the horses down the ant holes in the pasture. It is working. Maybe have to do it several times depending on how long the hive has been there. Just a tablespoon or so everytime I see activity. Pretty soon they seem to be gone. I use Bronco or Zonkit....cheap LOL
Be careful if using Seven dust........our vet said it's an organophosphate and no longer considered safe for animals. (I didn't know that)
Since moving to Texas, I have been very up close and personal with fire ants! I had 16 bites on my right leg. I went to the pharmacy, asked what to use on the bites and (I was taking Benadryl), and was told just plain old household ammonia. It works! At the local feed store, they told me sevin would work on the ant hills. I have always been told that it was safe, and I even powder my dogs and their bedding with it. Anyway, I have 5% Sevin dust, I have put it on fire ant hills, and next day, no ants! It gets on their bodies and they carry it to the queen. Sevin will also kill Japanese Beetles. I will have to ask our vet about sevin no longer being considered safe for animals, but till I hear it straight from the "horses mouth", I will use it on those blasted ant hills! I am so allergic to so many insects, and anything that saves me a problem and is safe is worth using to me. Thanks for the heads up on the sevin. I will call the vet about it right away.
Oh, I tried the vinegar recipe, just scurried them around, but did not kill them. I know boric acid works, but I am afraid it is poison to the animals.