Black knuckle on Whitney crab apple tree

I have a black spot in the crotch of two of my Whitney crab apple trees. Not sure exactly what it is potentially Black rot? Does not appear to have canker. Would love any feedback I hate to cut the tree down as it’s healthy otherwise but don’t want them to infect the rest of my trees. Also a very tough spot to cut out and do not want to use chemicals if possible

Three questions

1. What has the weather been like in the last few weeks?

2. Did make the wound and so have you used the tools on any other plants?

3. How old is the tree?

It’s been dry this spring and we recently received 4” of rain. The spots were there while it was dry in the spring though. These trees were bought in the nursery just two years ago. They are young apple trees. They came with that knuckle there I’m guessing it was a branch that was pruned at some point at the nursery.Just wanting to make sure it’s not some disease I need to worry about that could affect my other trees

If there are no bugs around the wound, my best guess is slime flux.