Oak wilt is a lethal disease of oaks at epidemic levels in Central Texas. The disease is caused by the reaction of susceptible oaks to the fungus Ceratocystis fagacearum.

The fungus causes the water conducting system of the tree to become plugged so that the tree wilts and drops its leaves. Most infected oaks die within weeks or months.

When one oak is infected with the oak wilt fungus, it transmits the fungus through the roots to surrounding trees. Oak wilt can keep spreading until the entire neighborhood is an "oak wilt disease center" with hundreds of dead and dying oaks.

Oak wilt has a high mortality rate (85-100%), it spreads rapidly (an average of 75 feet per year) and it is difficult to control (roots must be cut in a wide circle around the infected oaks). Oak wilt is considered by many scientists to be the most devastating tree disease in the south.