Q.I Think My Husband Has Killed My Peach Tree With Severe Pruning
He pruned last year. There are now numerous cankers and leaves are yellow and falling off. There are also mushrooms on branches. This tree has been very productive for several years, but this year only a handful of peaches.
Certified GKH Gardening Expert
Probably the severe pruning itself did not make the tree have problems, but anytime a tree has open wounds, disease can get in - just like it can with people.
It sounds like the cankers are the root of the problem. There are several kinds, so I would reach out to your local extension service and see if they can help you identify which is specifically attacking your tree and how best to treat it.
This article will explain more about tree cankers: