Urnula craterium has been described as the perfect or sexual stage of the fungus causing strumella canker. The urnula fruiting body is cup-shaped and grows on infected branches and stems that have fallen to the ground. Identifying the Injury. Diffuse cankers develop on smooth-barked saplings and rapidly girdle and kill the trees. Targetshaped cankers are more common and are formed by the alternation of cambium killed by the fungus around the canker perimeter and then the formation of a callus ridge by the host.
Cankers can reach several feet in length.
Oak killed by strumella canker. As with many canker diseases, the fungus usually enters the tree through a branch stub. The remnants of this stub can be seen at the canker center. Frequently, diseased trees bear multiple cankers. However, cankered trees should be removed during sanitation or commercial thinning operations.