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Oak Wilt
Distribution of Oak Wilt in
the United States
Symptoms and Signs of Oak Wilt
Symptoms of oak wilt include chlorosis, bronzing
(necrosis) of leaves, flagging,
wilting, premature leaf fall and death.
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Circular areas or patches of dead trees
are characteristic of oak wilt as seen in these aerial photographs.
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Typical leaf symptoms. This leaf and
others like it would have been shed from the tree.
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Vascular discoloration is typical of trees
with oak wilt. Note that the discoloration is
limited to the outer sapwood region.
Bark on diseased oaks may be cracked open
by a structure produced by the fungus
called a pressure pad. To the right is a
side-view of a pressure pad.
Pressure pads: Note the mycelial mat
surrounding the pads. It is here and on the pad that
the reproductive phase of the fungus is formed.
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One means of dissemination of Ceratocystis
fagacearum is by insects. Here two sapfeeding beetles (nididulids)
are feeding in the area of a pressure pad. Spores (conidia and ascospores)
of the fungus are sticky and easily adhere to the body of the insect.
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Perithecia of Ceratocystis fagacearum.
Note the whitish masses of sticky ascospores.
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Cultures of Ceratocystis fagacearum
isolated from diseased trees. The fungus produces mycelium that is distinctive
in color and odor.
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Another means of spread of this fungus is
through root grafts.
Control of Oak Wilt
A means of control of oak wilt is to eliminate
root grafts between diseased and healthy trees.
This may be done mechanically as shown by
these slides. Removal of susceptible oak species
within 50 feet of a diseased tree is practiced
in many states. Stumps of cut trees are treated with a herbicide
to prevent sprouting. Pruning and forest activities that could result
in wounding during
spring or summer should be avoided.
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This website was prepared by Becky Bernard.
Last updated on 04 February 2008 by M.J. Munster |
