Fusarium?

There is a volunteer mimosa tree in my yard where a nearly dead dogwood was cut down a few years ago. It showed up a year or two after the dogwood, did well for two years, but now the leaves are turning yellow and dropping off. From what I've read it is probably Fusarium fungus, but all other theories are welcome. The tree is surrounded by black raspberry bushes and those closest to it bear hard, stunted, inedible fruit.

Before this tree sprang up I'd wanted to plant a fruit tree in the spot. Will it be doomed to suffer the same fate and is there any way to treat the area to get rid of it? I'm going to chop down all the affected berry canes as a first step.

TIA for any help.