| Hypoxylon canker is caused by an opportunistic
fungi, Hypoxylon atropunctatum. Hypoxylon is
unable to cause disease in healthy trees but is quick
to colonize weakened or dying bark and wood.
Oaks in the black oak group (pin, red, black, scarlet,
and willow oak) are more susceptible than those in
the white oak group (burr, chestnut, swamp white,
and white oak). The disease is also found as a
saprophyte (living on dead wood) on basswood,
beech, hickory, hornbeam, maple, and sycamore.
Symptoms and Diagnosis
Yellowing and wilting leaves may signal the onset of
the disease, but these symptoms are merely general
indicators that the plant is under stress and are not
necessarily caused by the fungus. The most
recognizable sign of a problem is the sloughing of
patches of bark on the branches or trunk which
exposes a silvery or cushiony layer of fungus. Prior
to the bark sloughing, sunken or depressed areas
appear in infected areas where the fungus has killed
the cambium. Dead or dying limbs in the tree may
also be the result of hypoxylon canker.
Life Cycle
The fungus enters the tree through wounds on the
branches or trunk and grows in the sapwood where
it kills this conductive tissue. There is evidence that
the pathogen may invade young trees but not cause
a problem until the tree is under stress. Infected
branches progressively die back as the fungus moves
downward. Dead, sunken patches develop on larger
trunks where the advancing fungus kills the
conducting sapwood. Trees may die in one to two
years or sooner if the early stages of the disease
go unrecognized.
Integrated Pest Management Strategies
1. There is no effective control for the disease. If
over 15% of the crown is infected, cut the tree to
ground level and burn or have a hauler remove it
from the site. Since the fungus can remain active
in dead wood, do not chip the wood and use for
mulch. Also, any wood burned as fuel should be
used quickly.
2. If 15% or less of the crown is infected, prune
out all infected branches and cankers. Dispose of
as noted above. Also improve the health of the
tree by watering and fertilizing. |
