I have noticed that my Post Oaks have strange little orange sac like things on the underside of the leaves. Can anyone tell me what these are, are they common and are they a threat to the health of my trees? If they are bad for the trees how do I remedy this situation. Two of these Post Oaks are estimated to be the oldest of their species in Denton county so I'd hate to lose them.

Have you opened one by chance to see if they are a cocoon of some sort or if they are galls?

They are solid fuzzy spheres with a tiny green center. They have a similarity to the fuzz on a cat o nine tail. Densely packed fibers all running parallel to each other, emanating from the center outward.

They are most definitely galls.

Check this out: http://badeggcollective.blogspot.com/20 ... -gall.html

Thanks Sandi. The linked article you provided was interesting but I didn't glean from it whether these galls are harmful to the trees. I'm rushed this morning, perhaps I missed something? Will this problem be taken care of when the trees drop their leaves?

Thanks again.

If you click on the main logo up top, then go to Library and click on 'G' for galls you'll see more info from Howard. Here's a bit:

The galls below on the back side of the live oak leaves are no serious problem unless there is a heavy infestation. In that case the tree is definitely in stress for some reason. Apply the Sick Tree Treatment and the population of these galls will diminish.