Any chance you are fighting fire blight? I had that hit my thornless when they were still amongst the living.
Yep, copper spray is the treatment. We had fire blight hit our fruit trees and a few of our thornless blackberries but it was tough on the trees. Don't know how many we lost.
Not sure. I googled fire blight but the pictures that come up don't really look like what I have.... I have two peach trees nearby and they look perfectly good but I do try to spray them religiously with Bonide Fruit Tree Spray. I sprayed the blackberries too but they continue to deteriorate so I'm going to up the game with copper fungicide instead.