My plum trees are wracked with black knot.  That’s a gnarly looking fungus that infects a branch, and kills the rest of the branch.  Close up, the corruption looks like this.

Two of my plum trees have always struggled with this, and there isn’t much that can be done beyond pruning.  Both trees have been pruned before, but this year, it was bad.  Here is a before and after for one tree.

When all the leaves are gone, it’s easy to see the infection.  Everything that was infected, was cut off.

The tree may not recover, but it will be left for a couple of years.  Fruit trees can be pretty resilient.

The infected branches have to be burned or buried.