Are you seeing oaks with brown tips? It could be caused by twig borers, tiny beetles that bore into branches.
These borers introduce a fungus that kills the branch from the point where the beetle has entered the branch to the branch tip. Often this is the last one to 2 feet of the branch. The fungus serves as the food source for the immatures. The entrance holes are very tiny and hard to see with the naked eye. However, a quick look under a microscope or hand lens may reveal the tiny, round hole, almost machine drilled in its appearance.
Twig borers are common on many kinds of trees in our area, including red maple, oaks and some other trees. The damage is usually more cosmetic than threatening to the tree. Eventually the dead branch tips drop to the ground. Insecticidal treatment is usually not necessary.
More information about twig borers can be found here: http://www.entnemdept.ufl.edu/creatures/trees/black_twig_borer.htm