Weird knobs on willow oak tree
Can you please tell me what these are? The willow oak is relatively young, maybe 25 feet tall. There are about 8 - 10 of these on it. They are hard, dry, and when cut open have a solid fibrous interior. Doesn't seem to be a larvae. Can they hurt the tree? Should we cut off the tips of branches that have them (they cannot be pulled off the branches).
This looks like a type of stem gall. They do not seriously affect the health of the tree. No chemical control is recommended. Prune the branch below the gall. Dispose of in the trash. See our website for more information on galls http://extension.umd.edu/hgic/shade-tree-galls