An annual canker that occasionally is found in large numbers on sugar maple, it first appears as a sunken area on stems or branches, with dead cambium underneath. As callus tissue develops around the dead area, the sunken bark falls away, exposing the underlying wood. Subsequent callus formation may completely close the lesion, and normal bark may form again during one growing season.

These cankers are lenticular and can be from 0.5 inch (1 cm) to several feet long, and from 0.5 to 8 inches (1 to 20 cm) wide (Fig 87). They provide openings for secondary decay and stain organisms. Similar-looking cankers have been observed on red maple, black cherry, red oak, and white ash.

Cankers develop between late fall and early spring (during the dormant season). A species of Fusarium, probably F. solani, is suspected as the causal organism. This fungus is a common inhabitant of soil and of healthy bark of trees, apparently infecting bark wounds that extend to the cambium. Trees stressed by factors such as windstorms, sudden drops of temperature, or insect wounds are affected. Tree growth usually is not impaired and the lesions close over after a good growing season.