I have a dwarf honeycrisp apple tree that looks healthy. the graft union looks fine except the root part has little bumps all over it. Is this just a certain type of root or something to worry about?
Sounds like burr knots, which in my understanding are basically where the tree is trying to send out more roots but finding that the location has no soil so the process stops at the little bump stage. If you mound soil around the burr knots then more roots will grow. If you just leave the tree alone, it might be just fine, although there are some organisms that sometimes bore into these burr knots and can cause disease. Personally I wouldn't worry too much unless I saw holes bored in there. Might be something to monitor on an annual basis but it will probably be fine is my guess.