Question
I live in Springfield, VA with 8 oak trees in the back yard.  This year, there are small "balls" on the underside of the leaves.  They are also falling to the ground and it sounds like it is raining as there are so many. We know it isn't raining because we are in a drought.  The local nursery said they are "galls" ~~ in Googling "galls" it comes up with not a good explanation but rather that "galls" are larger.  Do you have any insight on what we are exeriencing?  

Thank you ~~
Cheron

Answer
This sounds like a leaf gall insect. These insects will secrete a chemical on the leaf and lay eggs and the chemical will cause the leaf cells to grow over the eggs forming a gall. When the eggs hatch the gall will fall off. These gall insects cause very little damage as far as the health of the tree goes. They may cause the leaves to fall a little sooner than normal. I would not worry with them the population will vary greatly from year to year and next year you may not see any galls. There is not practical control measures and really none is needed.