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OAK WILT DISEASE
Special - March, 2005
By Bill Cook
Thinking about
those construction or landscaping plans for this spring? If so, remember to
avoid damaging oak trees. Be careful with that lawnmower! Human-caused wounds
is one of the most common ways to spread oak wilt. The moist wounds attract
spore-carrying sap beetles which carry disease spores from infected trees.
Once an oak is
infected it cannot be saved.
The standard
time to avoid oak injury is May through July. In most years, the spore generating
fungal pads have dried-out by then, but not always. Last year, fungal pads were
active into September.
Oak wilt is firmly
established in the Shakey Lakes region of Menominee County. Additional oak wilt
epicenters are scattered along the Menominee River and in the Iron Mountain
area. In 2004, a new eradication effort began. It will likely be continued this
summer.
Last fall, about
50,000 feet of root-breaking trench was plowed. A hundred epicenters were treated.
Identification and treatment of oak wilt pockets will need to continue for at
least another year or two if we hope to achieve a good measure of control.
When an oak wilt
pocket is identified, both overland and underground disease spread must be stopped.
Overland spread can be controlled by removing and properly disposing of infected
trees. Underground spread is treated by a vibratory plow that severs roots down
to five feet. Root systems must be broken due to the root-grafting habit of
red oaks, which would otherwise spread the disease from tree to tree.
Oak wilt can
be recognized by rapid wilting of leaves beginning at the top of the tree. Oaks
killed last year will display spore pads that rupture the bark, usually evidenced
by a slight swelling and a vertical crack. The spore pads are often called pressure
pads due to this behavior.
The combination
of drought and attacks by two-lined chestnut borers can sometimes be mistaken
for oak wilt, especially on sandy soils. However, the dying process is usually
longer and recently dead trees do not form the spore pads.
Gypsy moths can
mask the leaf effects of oak wilt when the trees are defoliated in June. Many
oak areas were loaded with gypsy moth egg masses in the fall of 2004.
The disease can
easily be transported in logs and firewood. Harvested oak from infected stands
should either be processed immediately or tightly covered by tarps. Oak wilt
is one more reason why the movement of firewood should no longer be done without
consideration for the potential of spreading insects and diseases.
If construction
or landscaping is absolutely necessary during the spring and early summer, oak
wounds should immediately be painted. Any commercial wound paint will work,
but immediate means within minutes. Letting the task go until the next day can
significantly increase the risk of infection. Oak wilt prevention is one of
the few reasons that tree wounds should be sealed. It is not a normally a beneficial
practice.
Should your oak
trees display symptoms of oak wilt or if you would like more information, contact
Bill Cook at cookwi@msu.edu or 906-786-1575. His office is at the U.P. Tree
Improvement Center near Escanaba.
The oak populations
in the Upper Peninsula are vulnerable to this disease. Oaks are about the only
trees that produce hard mast along the Menominee River. The acorns are a valuable
commodity for many species of wildlife. Oaks also have other important ecological
roles and are popular trees among landowners for many reasons. Please make every
effort to help control the spread of oak wilt.
- 30 -
Trailer
Bill Cook is an MSU
Extension forester providing educational programming for the entire Upper Peninsula.
His office is located at the MSU Upper Peninsula Tree Improvement Center near
Escanaba. The Center is the headquarters for three MSU Forestry properties in
the U.P., with a combined area of about 8,000 acres. He can be reached at cookwi@msu.edu
or 906-786-1575.
Prepared
by Bill Cook, Forester/Biologist, Michigan State University Extension, 6005
J Road, Escanaba, MI 49829
906-786-1575 (voice), 906-786-9370 (fax), e-mail: cookwi@msu.edu
Use
/ reprinting
of these articles is encouraged. Please notify Bill Cook.
By-line should read "Bill Cook, MSU Extension" Please use the article
trailer whenever possible.
Michigan State University is an affirmative action equal opportunity institution. The U.S. Department of Agriculture prohibits discrimination on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital status or family status. (Not all prohibited bases apply to all programs.)
This website is maintained by Bill Cook, Michigan State University Extension
Forest in the Upper Peninsula. Comments, questions,
and suggestions are gratefully accepted.
Last
update of this page was
22 September, 2005
This site is hosted by School of Forest Resources and Environmental Science at Michigan Technological University.
