Q: My crabapple tree has a big rotten hole in the trunk where a limb broke off. The tree is about 2″ DBH and about 15-20 feet tall. Should we go ahead and cut the tree just below the hole?
A: I think it will be best to cut the trunk below the hole. The damage is big enough to permanently weaken the trunk and it will eventually fail anyway.
I see that a side branch is turning vertical, trying to become the new central leader. It will be much stronger than what you have now.
In a few years there will be a “J” bend there in the trunk but the tree will be fine.