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Oak Wilt in the U.P.
Article #148, September 2009
By Bill Cook

Fall is the season for the great northern color change and the beginning of the deer bow season. It's also the time to treat areas of oak wilt that have been identified and prepared this summer.

For about a week in early October, a vibratory plow operator will be slicing through oak roots to isolate diseased areas underground. The plow will reach five feet deep. Before next spring, all the oak within the treatment area will need to be removed to prevent overland spread of the disease.

Oak wilt is an exotic pathogen that has been around the Midwest for decades. In many areas of Michigan and Wisconsin, the slow but certain spread has reached epidemic proportions.
Similar to Dutch elm disease, oak wilt is fatal. There are very few survivors.

The disease first enters an oak stand from small insects that carry the disease spores from a nearby infected stand. Once within a stand, the fungus spreads through the root systems. Species in the red oak group tend to graft roots between trees, an avenue exploited by this disease. Trees in the white oak group don't typically display root grafting, but if infected overland, they too will die.

At some point during the growing season, an infected tree will lose all its leaves within a few weeks. Any residual green branches or green sprouts mean something other than oak wilt has attacked the tree. Oak wilt fungus requires live tissue to survive. So, during the following spring and summer, after the disease kills a tree, then the fungus will produce a fruiting body. These gray lumps tend to push up the bark forming cracks. With a hatchet, the fruiting body can be exposed. It's these fruiting bodies that attract sap-feeding insects that can spread the spores to healthy trees. They can also be transported with firewood.

Determining the proper distance between dying trees and healthy trees is a function of the size of the trees in question. The perimeter of the affected area is determined by these distances. Large oaks result in larger areas to be treated, as they have larger root systems than smaller oaks.

Once the perimeters have been established, the vibratory plow can be scheduled. The number of feet to be plowed depends upon the size of the forest health grant provided by the U.S. Forest Service - State and Private Forestry, as well as capacities within the Michigan DNR and MSU Extension. Landowners are responsible for only the removal of the oak. The set-up and trenching costs have been covered by the grant.

Since 2004 in Menominee and Dickinson Counties, over 26 miles of treatment line have been plowed at the price of $275,000. That's about two bucks a foot. A little more than half this amount occurred on private land, with most of the public land on state forest.

For the most part, the treatment appears successful in most places . . . so far. Each treatment line needs to be monitored for at least three years after plowing.

However, there have been locations where the disease has remained despite treatment. In some places, inoculum from nearby untreated stands can infect healthy stands next to treated areas. Newly infected trees are overlooked because they don't show symptoms until the following year. Sometimes, large underground boulders, high bedrock, or other obstructions can prevent complete trenching, despite the diligent and conscientious efforts by contractors. Other times, there may have been an error in setting the distances between infected and healthy trees. And then, the distance charts are designed to be 95 percent certain, not 100 percent.

While treatment cannot guarantee containment of the disease, lack of treatment will guarantee the death of all oak within a stand. Doing nothing will have an impact. So, the decision of whether or not to treat oak wilt depends on the value a landowner places on the oak resource, and how well a landowner might want to get along with neighbors. The partnering agencies remove most of the financial obstacles. The final decision belongs to the landowner.

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.

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