Cankers are localized dead areas in the bark of stem, branches, or twigs of many type of trees and shrubs. Most cankers are grown by fungi, which grow between the trees bark and wood, killing the living portion of the bark. Cankers are very destructive and hard to manage. The fungi girdles stems of the plant host.

One of the most damaging cankers in the southeast is the Oak Hypoxylon Canker (fungus - Hypoxylon atropunctatum and other Hypoxylon spp. Pictures below). The disease is first evident as a dieback of one or more branches. The foliage of the diseased limbs turns yellow and dries. This die back continues from branch to branch through the stem until eventually the tree dies.

Hypoxylon canker causes a dark brown discoloration of the sapwood. With age the infected wood is lighter in color and has black zones or patterns in the wood when observed in cross section.

Hypoxylon canker occurs primarily on trees which are or have been in stressed conditions. Trees which have been damaged by excessive fill soil are often attacked by this organism. It is also suspected to be a fungus that can invade on oak wilt-infected trees.