Forest Health Protection, Southern Region

Importance. - Many hardwood trees are susceptible, but oaks and hickories are commonly infected. Degrade and decay of hardwood lumber are the most important losses.

Identifying the Fungi. - Fungal fruiting bodies (conks) may be associated with the cankers and are variable. They can be toothed or pored; shelflike or flat, shortlived or persistent. Poria spiculosa produces sterile fungus material in the canker and only produces a fruiting body after tree death.

Identifying the Injury. - Cankers and associated localized decay vary in size, shape, and degree of callus formation. Dead branch stubs usually are located at the centers of the cankers.

Biology. - Airborne spores produced by the conks land on wounded areas and initiate new infections. An internal decay column can extend rapidly, sometimes by as much as 6 to 10 inches (15 to 25 cm) annually. It normally exceeds the external canker face in length. The fungus interrupts normal decay resistance processes and eventually kills the cambium. Callus tissue may be killed when the canker expands.

Control. - Removal of trees with cankered main stems provides more growing space to surrounding healthy trees and can also reduce conk and spore production. The pruning of declining branches may help prevent cankers in urban trees.