Hypoxylon canker

Hypoxylon canker is a common disease of hardwoods, especially species in the red oak group. It is often one of several factors ultimately responsible for tree death. A disease of the inner bark and sapwood, Hypoxylon damages tissues used by the tree to conduct water from soil to the leaves. Vigorous, healthy trees are colonized by the fungus, but only damaged or stressed trees develop cankers and die. Outbreaks of this disease tend to follow severe drought.

Initial symptoms of the disease include a noticeable thinning of the crown, small patches of brown leaves and branch dieback.

As the disease advances, large areas of bark fall off the branches and trunk, revealing a thick, dusty fungal mat with tan spores. (Photo by Ronald F. Billings, Texas Forest Service, bugwood.org.)

Eventually, the fungus turns silver or gray as it matures, giving the appearance of thick paint on the side of the tree. (Photo by Robert L. Anderson, USDA Forest Service, bugwood.org)