The food grade DE I am currently using was WAY too expensive. It came from Freshwater Organics. The bag says it kills fire ants. Custom Milling's price is MUCH better, though I've heard Brian say the shipping made it cost prohibitive for him. I will find out if it's a better price with shipping when I run out of the original 50 lb. bag I am using now. I still have probably 35 lbs. or better.
I haven't tried stirring up the DE in the beds, because I was trying not to disturb the nests. When I use it, the mound seems to crust over, but the slightest amount of moisture, even dew, seems to reactivate the mound. I now have multiple small mounds around the whole perimeter of the largest mound I'm treating nearest the coop. It is around the base of a tree that shades the south side of the run. Could be I'm not using enough, because a few of the smaller mounds near the vegetable garden did not spread or come back.....yet. The larger mounds are driving me crazy.
Btw, I have tried shoveling from mound A to mound B. The mounds need to be close, or the ants will move up the shovel handle and eat you up before you accomplish much.
My older birds avoid large mounds. They scratch at teeny, tiny mounds just beginning where you can still see the original hole in the ground and just a few grains of mound still flat around the hole. Once they peck at a fire ant there, they leave the area.
I am going to use the Orthene powder the county agent advised - 1/2 tsp. per regular sized mound and 1 tsp. per large mound. It is a wettable powder, but he told me to punch salt and pepper holes in the seal and sprinkle it dry without disturbing the nest and only on the mound itself(unlike Amdro which you use in a 3 ft. perimeter around and up to the mound). He swears they will be gone and not come back....ever! LOL! A canister is $9.99 at Home Depot, and the county agent says I will probably only need ONE CAN a MONTH! That will be a HUGE savings compared to Amdro which works, but takes a great deal more per mound and is much more expensive.
Of course, if your neighbors have them and don't treat their mounds, you will get brand new fire ant beds anyway.....never-ending money trap....killing fireants! After several rains, it should be safe to let the chickens eat grass where the Orthene was used.
Brandy is the only chicken I have who free ranges and I follow her around when she is out, so maybe she can come out before it rains. When the others come out of the pen, they stay in the small strip between the pen/coop and barn. There are no fire ants there.....yet. I keep that strip sparsely sprinkled or dusted with the DE (Miss Prissy's great idea for a duster - panyhose!) all the time, so maybe they won't build a mound there.