Importance. -- Hypoxylon cankers affect most oak species in North
America. Both H. atropunctatum and H. mediterranium have
been reported in oaks. They affect mainly trees that have been stressed
by wilt, drought, construction damage, or other injuries. Limbs and
boles weakened by Hypoxylon spp. can be a safety hazard in high
Identifying the Fungus (figure 66). --
Hypoxylon spp. can be identified by the light- to dark-colored
crusty fungus tissue (stromata) over the cankered area. Numerous small
black fruiting structures are embedded in the stromata.
the Injury. --
Bark sloughing and decay are associated with Hypoxylon cankers. Affected
trees are subject to wind breakage.
The fungus infects stressed trees through wounds and either produces
a canker or quickly kills the tree by colonizing the sapwood. Fruiting
structures develop on the cankers and ascospores are discharged into
the air and spread to new infection sites. Hypoxylon cankers are generally
secondary to some other disease or stressing condition in trees.
Remove cankered limbs before they fall on someone, and to reduce the
amount of inoculurn for new infections. Maintain tree vigor and avoid
wounding and stubbing of branches to minimize conditions favoring cankers.