Question
I live in Central Texas and have several trees on our property that I think are some type of scrub oaks.  Several of the trees have something that looks like a berry sitting on the leaf.  They are about the size of a grape and are yellow to red.  A friend told me that they were a type of fungus.

Answer
These are leaf galls caused by a small insect. The insect lays its eggs on the leaf and secretes a chemical that causes the leaf tissue to grow over the eggs. Leaf galls cause no real health problem with trees. IF they are abundant they could cause the leaves to drop sooner than normal. There is no need to try and control this insect since it causes no damage to the tree. Gall insect populations vary greatly from year to year and next year you may not see any galls. Any control would have to be applied before the eggs were laid and this would be very difficult to time the spray to the egg laying. Do not worry about this.