
Hypoxylon canker is a common disease of oaks that can affect several species of shade trees. These fungi take advantage of stressed or declining hardwood trees. Infected trees can be in various habitats, including recent or well-established residential areas and forest trees. The canker areas often become quite obvious after the trees drop their leaves for the winter. The bark usually sloughs off, often near the trunk or major branches, revealing the black or pale gray fungal mat beneath. The fungus usually kills the cambium and portions of the sapwood, creating the potential for breakage. If cankers girdle the branch, the branch will die. The key ingredient to canker-free trees is prevention. It is important to avoid tree wounds. Construction injury, herbicide damage, and site-related stresses (drought, etc.) contribute to disease onset. Homeowners need to promote vigorous plant growth by correct fertilization and irrigation.