Question
Our post oak tree has been covered with tiny pea-sized orange fuzzy balls.  They are on the leaves and the twigs.  The tree seems to be losing its leaves faster than normal. These orange fuzzy balls on lying thick on the ground.  What are they?

Answer
These are called Oak wooly galls. They are caused by a tiny wasp insect. The wasp lays its eggs on the leaf bud and the eggs hatch and the tiny larvae drill into the leaf and secrete a chemical that forms the wooly gall. The insect has gone by the time most people see the galls. The galls really do little damage to the tree. The leaf will turn brown where the gall is and may drop prematurely. On a small tree they could cause some growth loss but not enough to harm the tree. To spray for the insect you would have to spray just before the leaf buds break in the early spring. It is not worth the effort since the tree is not damaged. I would fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb of fertilizer per inch of trunk diameter--scatter this evenly around the tree and water in good. The population of wasps varies greatly from year to year so next year there may be no sign of them at all.  This will make the tree healthier and even if all the leaves were infested there would be no growth loss.