The Case of the Brown-tipped Oak
The client was concerned about her oak tree. She had noticed that the last several inches of some of branches were dead, with brown, lifeless leaves. She brought some branch samples to our Lawn and Garden Help Desk, fearing the worst. Was this something that would spread? Would it kill the tree?
Looking at the damage, my first suspicion was 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 (young). The entrance holes are tiny and my middle-aged eyes, even with the help of reading glasses could not locate a hole. However, a quick look under the microscope revealed 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