Woodland, Your peaches are damaged by either Oriental Fruit Moth (OFM) or Plum Curculio (PC). They have some differences but the end result is the same - both insects cause most damages on peaches (fruit). You don't see them because larvae are hatched inside the fruit. Cut the fruit up, you'll see damage inside. Sometimes, the larvae are still there. Sometimes they are gone to build the next generations of trouble. Fruit that are damaged will drop prematurely. Pick up all those fruits. Throw them in trash. Do not compost or let them lie around on the ground. Don't let those buggers go underground to build their life cycle. If you spray, you need to time it before you see damages. Spray when tiny peaches are formed. The longer you wait, the more chance that they will beat you to your peaches. Once you see damages on your fruit, it's too late. Pick them all off and wait for next year. If you see some "clean" peaches left on your trees, you can safe them by spraying. Spray organically would be with Surround, a kaolin clay product. Spray chemically, I use Triazicide Once and Done, a product by Spectracide Others use other pesticide that work for them. Greenhouse - your could have both borers and canker. For borers, look around soil line or below for holes with oozes. I use a coat hanger wire and try to kill borers in the holes. Some spray with Triazicide, mentioned above. I have not need to spray for borer yet. For canker - you don't have much choice but make sure a tree is healthy and hope it will heal itself. If you read any post about peach problems on this forum, you will come across the following problems: OFM and PC damages, borers, Peach Leave Curl, canker and shot holes. Those are the prominent problems most grow peach growers have to deal with. Keep reading those posts, the problems and answers are similar.

do you think it will grow back from the base only or the tree itself will come back? it's been leafless for about 2 weeks. i had a dawn redwood sapling that i thought had died but kept watering it & it did come back so i've not given up on this tree yet.

Yes, it's likely bacterial canker. Check this link from UC Davis: http://www.ipm.ucdavis.edu/PMG/r602101011.html

Are those branches dead or still green and flexible? When inspecting the trunk from the bottom up, do you see any blobs of sap, saw dust, or holes? Any sun damage on the leafless branches such as cracked flaking bark? Are there buds on the bare branches that look like they could push out new growth?