I just found this growth on my Stanley plum tree. Can anyone ID it? My first guess was black knot, but it doesn't look like any pictures I can find, even the few pics I've seen of early stages.
I'm not sure whether you can tell from the picture, but it looks like this burst right out from inside the bark. It also seems like it came out of nowhere. We have a row of dwarf stone fruits, and when I found a small bit of something "black knot-ish" on one of them this winter, I went through the rest very carefully. There was nothing at all to be seen, and now it's a good 6 inches long. How on earth am I supposed to keep ahead of that?

Also, since I assume I need to prune this out, what are the easiest ways to clean the pruners afterward?