Oak wilt is one of the most destructive tree diseases in the United States. The disease has killed more than 1 million trees in 76 Central Texas counties. Oak wilt is an infectious vascular disease caused by the fungus Bretziella fagacearum. The fungus invades and disables the water conducting system in susceptible trees. All oaks can be infected with oak wilt, but some species of oak are more susceptible than others. Red oaks, particularly Spanish oak (Quercus buckleyi), are very susceptible to the fungus. White oaks, like post oak (Q. stellata) and bur oak (Q. macrocarpa), are resistant to the fungus and rarely die from the disease. Live oaks (Q. virginiana and Q. fusiformis) are intermediate in susceptibility to oak wilt. However, they are seriously impacted by the disease because of their tendency to form root sprouts that result in a vast interconnected root system allowing the disease to easily spread to adjacent trees.