We have green golf ball size growths near the top of an oak tree. What are they and how do we get rid of them?

Sounds like galls and Howard says they do not hurt anything.
Richard Spitzer

I have the same golfball sized orbs on my oak tree. I removed one and took it to the Dallas Natrualist meeting, I was told it was cauused by a wasp sting and it contains the egg of the wasp. I cut one open and it was filled with a dandilion like seed we see floating around in the spring and summer.