We've had quite a bit of rain during the past week so what passes for my "lawn" required "mowing" this morning. As I was buzzing along with my hopped-up string trimmer (all that I need to handle most of the weeds out there!) I noticed these galls on one of my oak treelings. Most are in the 1/2" size range but one monster is nearly 2" across. My other oak treeling is as of now free of galls. What's most amazing is that last week these galls *were not present* on the tree.
These are called "oak apples" by the locals and are equally common on all the types of oaks that grow well in my area: live oak, Spanish, red, white, and a few others. Healthy trees can withstand a modest load of galls with no ill effects. After the adult Cynipid wasps hatch out in December the galls will dry and I'll collect them for dyestuff - from my trees and from any other infestations I find.