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May, 2004  
By Bill Cook

     Don’t prune those oak trees and avoid any activity that disrupts their root systems!  This is prudent advice for those who wish to slow the progress of a tree disease called oak wilt.  Spring and early summer are when the fungal spores and traveling beetles are most prevalent and the disease most likely to spread.  Oak wilt is a fungus in the same genus as Dutch elm disease. 

     The “red oak” group of oaks is most vulnerable.  In our region, that means northern red oak and northern pin oak.  Menominee, Dickinson, and Delta Counties have some of the largest concentrations of oak in the Upper Peninsula.  The “white oak” group of oaks is less vulnerable.  White and bur oak are also less common.

     This time of the year, construction wounds many trees.  Wounds can also occur from a wide variety of reasons such as pruning, wind, wildlife, etc.  A wounded oak attracts certain species of spore-carrying sap beetles.  Once infected, the oak will die.  The fungus can then spread underground through the root systems.  Oaks have the peculiar characteristic of root-grafting with other oaks in the same taxonomic group.  So, the disease can spread throughout an entire oak stand from a single infection. 

     For unavoidable wounds, immediate application of tree paint is recommended.  Typically tree paints are not recommended for tree wounds, but oak wilt prevention is an exception.  Trees that must be removed should have the stumps immediately painted.  The logs should be sealed until winter under a plastic tarp with the edges buried.  This seal will keep the spores in and the beetle out. 

     Oak wilt can be identified by browning and wilting leaves.  The wilt usually begins at the tip of the leaf and at the top of the tree.  Samples should be collected and sent to a diagnostic lab for confirmation.  Browning leaves and a wilted appearance can be due to other health issues such as anthracnose and oak decline.  Recent droughts, two-lined chestnut borer, and gypsy moth outbreaks have weakened oak trees in the U.P. and northern Wisconsin.  Oak wilt pockets can often be identified by a dead center within a ring of dying trees.  Without treatment, the infected pocket will continue to grow.

     This summer, the DNR and MSU Extension will be identifying and treating oak wilt pockets in the southern U.P.  If you suspect you have oak wilt on your property, contact Bill Cook at 786-1575 (Escanaba) or your County Extension Office.  For more information about oak wilt, try the Internet at [www.na.fs.fed.us/spfo/oakwilt/jccamph.htm] or [http://cecommerce.uwex.edu/pdfs/G3590.pdf].

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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.

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