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Without seeing the problem, it's hard to diagnose. However, if the areas are on the leaf and are blisterlike and puckered, it may be oak leaf blister, which apears this time of year. This disease looks bad but does not harm the tree. The control for this would be to spray with a product containing Daconil, such as Ortho Garden Disease Control. But this must be done in the spring, when the leaf buds just start to swell, so you'd have to do it next year to prevent the problem the following year. Again, you really don't have to do anything, since it doesn't hurt the plnt.

The best tact would be to take some of the leaves in to a good garden center and talk with the garden center manager about the problem and what the solution might be.

If the growth is on the bark, it could be lichen, which also is harmless.