Jennifer, it looks like a fungal infection as a result of damage. I had a redbud that got bumped by the lawnmower and had a tiny (according to my husband) nick in the trunk. The tree did not survive.
It may be what is called apple scab...
https://ask.extension.org/ques...
You may want to e-mail or call and speak with your county agent/co-operative extensive service. Good Luck.
