Harlan:

Something else is responsible for your dead peach tree branches, probably bacterial canker or a similar infection. Ants are an effect of dead wood, not a cause. You can prevent or at least delay bacterial infections on peaches by thorough dormant spraying with a strong copper solution.

If you want to get rid of the ants, which are doing nothing but nesting in the already dead wood, spray the tree with Permethrin, an insecticide that is widely available on the consumer market. Permethrin is very effective on ants.

I don't know how old your peach tree is, but these trees rarely make it to 25 years before they succumb to branch-killing diseases. Many don't even make it to 20 in a humid summer climate like yours. That's the time to cut them down and plant a new peach tree.

I also don't know what you define as a "good" crop, but if the little peaches are crowded, they should be thinned to a minimum of 6 and preferably 8 inches apart so they grow up to be full-size, quality peaches. Remove all the smaller and insect-damaged fruitlets first, and leave behind the larger, fastest-growing, perfect peaches. If you live in an area where the oriental fruit moth is common, which you probably do, you will also have to spray the tree with an insecticide (Permethrin is also good for this), or bag the peaches in nylon shoe-store try-on footies to keep the OFM from ruining your peaches. I spray first, then install footies at thinning time.

OFM visits are easy to spot on young peaches, since they leave behind a little blob of pectin on the skin surface. The plum curculio leaves a small, crescent-shaped scar, and you don't want that either.

Don Yellman, Great Falls, VA