State university extension services are a great resource.
questions and answers about plum trees (both wild and domestic plums). The website is titled "Hortiscope" and it's a ten-year archive of a newspaper column written by Dr. Ron Smith, a horticulturist for the North Dakota State University Extension Service.
All of the information is written with a North Dakota slant, of course, but I found plenty of things in the tree Q&A pages that were relevant to Kentucky. For example, in answer to a question about how to kill stumps, Dr. Smith wrote, "Spray any sprouts that come up with Roundup. Drill holes in the stump and fill them with saltpeter." I am going to try his suggestion about saltpeter on a pesky mimosa stump in our yard that refuses to die.
I don't know where to buy saltpeter, but I do know that if I don't find it at the local farm supplies, I can call my local county extension office and ask!
Try this Google search to find a wealth of extension service and other government publications about trees and forest.