Strumella canker of hardwoods, caused by _Strumella coryneoidia_, most
frequently attacks trees of the red oak group. Other hosts include
species in the white oak group. Beech, basswood, blackgum, shagbark
hickory and red maple are also occasionally affected. This disease is
found in the East, from the southern Appalachians to northern New
England.
[Illustration: Strumella canker on black oak.]
Strumella cankers are of two types: diffuse, and the more common
“target-shaped.” The first develops on smooth-barked saplings and
rapidly girdles and kills the tree. Killing results because callus
tissue, which tends to heal over cankers, does not have time to develop.
Target-shaped cankers are more common. “Targets” are formed by the
alternation of killing of bark by the fungus around the canker’s
perimeter and the formation, in turn, of a callus ridge by the host
tree. The fungus is active usually in the dormant season, while
callusing occurs in the spring. As with most canker-causing fungi,
Strumella usually enters the tree through a branch stub. Cankers are
quite large and may reach several feet in circumference or length. The
presence of the causal fungus is revealed by dark brown, cushion-like
structures about one to three millimeters in diameter on the dead bark
and surrounding tissue.
No feasible control method is available under forest conditions.
However, the disease impact can be greatly reduced by removing cankered
trees during thinning operations.