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Oak wilt, caused by the fungus Ceratocystis fagacearum (Bretz) Hunt, kills oak trees. It has been found in 21 States, with considerable damage occurring in the Midwest. It was first recognized as an important disease in 1944 in Wisconsin (fig. 1) where, in localized areas (less than 100 acres (40.4 ha)), over half the oaks have been killed. Surveys in eight Wisconsin counties showed that about 11 percent of the annual growth increase of oak forests was offset by mortality caused by oak wilt.
No species of oak is known to be immune to this vascular disease. Infections have been found in 16 native oak species, including most of those of commercial importance. Species of red oak get the disease more frequently and succumb more readily than white oak. Plantation-grown Chinese chestnuts can also be naturally infected by the oak wilt fungus. Moreover, inoculation experiments have demonstrated that over 35 native and exotic oaks are susceptible, as well as American and European chestnuts, species of chinkapin, tanoak, and several varieties of apple.
Unfortunately, there is no known way to save an oak tree infected by the oak wilt fungus. The only way to maintain healthy trees is through prevention. Early detection and prompt removal of dead or dying trees and breaking root grafts between diseased and healthy trees are essential.
Abridged version of the Forest Insect & Disease Leaflet 29, U.S. Department of Agriculture, Forest ServiceCharles O. Rexrode (1) and Daniel Brown (2) 1 Principal Entomologist, U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station, Delaware, Ohio. 2 Forest Pathologist, U.S. Department of Agriculture, Forest Service, Southern Region, State and Private Forestry, Forest Pest Management, Atlanta, Ga.