What's a good way of killing fire ant mounds near my fruit trees?

pretty much any of the liquid over the counter sprays that attaches to the garden hose used for fleas will work, the active on the label will end in -thrin, (Permethrin, Lambda-cyhalothrin,Bifenthrin, etc.) can also use malathion, just has a nasty smell to deal with. These products are not systemic so the tree will not take up the toxin into the tree itself ...just drench the mounds down thoroughly and it is pretty much an instant fix. Some of the products used for fire ant control such as Orho Fire Ant Powder (Orthene)...Over and Out (Fipromil) and Merit (Imidacloprid) are systemic, so the toxin could be taken up into the trees, though the amount is probably not an issue, but why chance it. Amdro is also not labeled to be used around edibles, not sure if this is because it is also a systemic or if the company just never had the testing done for it to be used in these areas.

Here's what I did for the pile at my pomegranate tree. They have not returned:

Buy some diatomaceous earth. It's available at lowes/HD/where ever and should be less than $15.

Expose the site if it's not already (that is, clear away any rocks, junk, etc.).

Brew a full pot of double strength coffee. Boil a cup in a quart of water if you don't have a machine.

Take you hot coffe and DE to the spot. Then in quick succession, shove a stick into the fire ant pile (you want to p!ss them off), carefully pour the coffee directly onto down the stick, then surround all that in a thick ring of DE. Don't use the whole bag, but you want a very visible, 1in tall ring around it. If you have any leftover coffee grounds, dump those to the top of the pile when you are done.

This is particularly effective after it rains (like 12hrs afterward).

The coffee both burns and poisons the ants, who will try to escape over-ground; and when they do, they will be forced to run through the DE which slices their outsides up, causing them to dehydrate and die.

The fire ant pesticide sold at Ace Hardware is very effective. Just sprinkle it on and around the mounds, stir up the mounds a bit with a stick and in a few days, the mounds will be inactive and you can rake them smooth without being bitten.

Let them get their fill of the fruit and then they will no longer bother you because they will be full.

Bengle...Fire ant killer powder....If it can be used safely...Works good

Fight fire with fire