A serious threat to oak trees is the fungus Ceratocystis fagacearum, which causes Oak Wilt, a lethal disease to oaks, especially red oaks. Wood-boring beetles carry the spore of the fungus which actually causes Oak Wilt. Root Transmission may also be another way in which the tree is infested (by the underground root systems that often connect one oak tree with another). The fungus simply migrates from oak to oak by traveling through the vascular system of the roots in the same way that it spreads within the tree itself. The fungus clogs the vascular system of oak trees preventing the flow of water and nutrients. Once infected, the entire tree literally wilts and dies. The speed of the progression of the disease depends upon the species of tree infected.  Red oaks can die from oak wilt in as short a time as a month.    White oaks may survive as long as several years after infection. There is currently no cure for oak wilt.

Another common disease is Bacterial Wetwood that affects the central core or bark of many shade and forest trees. No effective methods exist to eliminate wetwood disease. Slime is the exudate generated from wetwood on which insects commonly feed. Wetwood-infected tissue does not greatly alter the wood strength of most trees. Prevention of tree stress is the best management approach. Effective control measures do not exist.