The other tree that's been problematic is the Santa Rosa plum. It's been growing extremely fast relative to the other trees and possibly too fast. A month or so ago one of the major branches broke, tearing at the joint to the main trunk. It must have had a weak joint, and as the branch grew heavier it tore at the seam.
I figured it could survive that damage and the other branches appeared fine. The tree was filling with fruit and looking good but then another branch went. Maybe I let them get too long and with the additional weight from the fruit it tore again at the seam with the trunk.
Now I'm not so sure the tree is worth keeping. The tear occurred near the other one making for a narrow section of the trunk. I'm considering removing the plum and pear trees and then replanting a new plum tree that I can prune more diligently as it grows. We were able to save a lot of the plums from the broken branch and the rest are maturing quickly. Looks like we'll be making plum jam this weekend.