Location: Cache Valley, zone 4b, Irrigated, 9" rain in badlands.
posted 1 year ago
That kind of growth is called a "burl". They can be caused by bacteria, fungi, insects, mechanical damage, freezing, genetics, graft incompatibility, etc, etc, etc. If the tree grows fine with them, then there doesn't seem to be any reason to try to treat them.
That is burr knot. It is the tree creating a place from which it can grow roots if needed. It is uncommon in selected apple varieties, but there are some varieties that are prone to it. Many rootstocks get it because they are selected partly for their rooting ability. One of the goals of breeding apple rootstock is to select varieties that root easily, but do not tend to form arial burr knots. They can be a problem. They tend to get larger, not smaller and can disrupt flow of nutrients up the tree, causing stunting or weakness. They can be cut out, but that is best done when they are very small. I have a video showing cutting them out of an already established tree, where it seemed like they would be enough of a problem that it was worth opening the trunk to probable infection to get rid of them. I haven't looked at it in a while, so I'm not sure how it turned out. Removing burr knots that size is rather traumatic though. It might be better just to leave them. Another common problem is that they can create a good place for borers to get in. What is the variety, or is it possibly a rootstock or seedling?
Steven: In the video, there were still little root spots on the area where it was cut off. Within the margin, in the center. I might have missed it but why didn't all of the center get cut out, too?
posted 1 year ago
The spots are in the wood, but if the cambium is removed the wood can't grow roots, shoots, bark or new wood until the bark heals back over. The idea being that the new bark will move in from the outside where there are no rootlet eyes, just plain bark. That's the theory I'm working off of anyway. I just make it big enough in diameter until I can't see any spots on the outside perimeter of the cut. I'll try to get out and take a look at those, and maybe do a follow up video.