Hypoxylon canker is common throughout the South on oaks and other hardwoods where it normally occurs on stressed hosts. The canker is caused by one or more species of fungi in the genus Hypoxylon. Found in the outer bark areas of living and healthy trees, the fungi are normally of little consequence. However, Hypoxylon can severely injure or kill trees weakened by factors such as drought, root disease, mechanical injury, logging or construction activities. These agents of stress enable the fungus to move into the xylem and produce cankers on the branches and trunk.
Apparently, the fungus is activated by reduced moisture in the xylem and bark. Once this low moisture threshold is reached, the fungi quickly spread. Especially in droughty areas, Hypoxylon fungi are often associated with tree death. Other fungi found in weakened trees may also play a role.
In recent years more oaks have been dying across the South. In many cases, the affected trees are victims of oak decline, a complex of environmental stress, site factors, and living agents, of which Hypoxylon canker is a major contributor.
QUESTION: We have large post oaks that have been dying of hypoxylon canker. We were told that there is no treatment for this disease. Do you agree? J.R., Double Oak
ANSWER: The fungal disease hypoxylon canker kills trees, but it is not the primary culprit. It simply finishes off sick trees. Trees weaken due to old age, bad soil, soil grade changes, physical injuries, exposure to herbicides and other chemicals, etc. After trees are in stress, Mother Nature sends in the cleanup crew: insects and diseases. Then, the Grim Reaper enters in the form of hypoxylon canker. If a tree’s root system hasn’t been damaged too much, you can use my Sick Tree Treatment to restore its health.