Homeowners in Grand Traverse County should be on the lookout for a deadly tree problem that is beginning to show up more frequently. It's called Oak Wilt disease. Oak trees infected with the disease suddenly "shutdown" or wilt and shed their leaves in mid-summer. By the end of the summer, infected oak trees die.
Over the last few weeks in Grand Traverse County, this year's "crop" of infected oaks has become very noticeable. Pockets of Oak Wilt can now be found in virtually all areas of the county. In addition, Oak Wilt is increasingly spreading across Michigan and is now becoming a serious forest and shade tree problem in many areas across the northern Lower Peninsula.
While Oak Wilt can attack trees in both the red and white family of oak trees, it is a much more serious pest of red oak trees. Typically, red oaks quickly wilt and die once they become infected with the wilt disease. The Oak Wilt fungus literally blocks all the water conducting tissue inside a tree and causes the tree to wither and die from a lack of water. White oaks are more resistant but can still become infected, but not as easily as trees in the red oak family.
The Oak Wilt disease is first spread into a new, previously uninfected yard or neighborhood by small picnic beetles that carry the fungus on their bodies. These beetles are attracted to fresh pruning cuts or other types of injury on oak trees that expose the inner bark or sapwood. As the beetles feed on the sap of these open wounds, they inadvertently transfer spores of the fungus from their bodies into the oak tree.
Once a single tree becomes infected with Oak Wilt in an area, the disease is further spread underground to other oak trees in close proximity through root grafts that surrounding trees create between one another.
Consequently, a patch of Oak Wilt killed trees usually occurs that takes on a somewhat circular pattern of tree mortality as the disease slowly is transferred from tree to tree via root grafts over a number of years. While this pattern is helpful in identifying Oak Wilt (in combination with other symptoms), it doesn't necessarily make it easier to treat and slow down the spread of the disease.
Currently there is no chemical pesticide available that can absolutely cure the disease once a tree becomes infected. Instead, the most common method of treatment is to slow the spread of the disease by severing (breaking) the root grafts between oaks trees. The most effective way to do this is by running 4-5 foot long (deep) trench lines underground in a series of plow lines between healthy and suspected, infected trees. All trees within the inner portions of the plow lines may eventually die, but the correct installation of the trench or plow lines severs the grafts between trees and halts the spread of the disease.
Given the expense of installing trench or plow lines, the most effective means of dealing with Oak Wilt by a homeowner is to prevent the disease from ever establishing itself in an area to begin with. While this may seem impossible, homeowners can help considerably in this regard by not pruning or injuring oak trees during the summer months (approximately from April 1 through Sept. 1) which is the most active period of infection. Experiences from Minnesota and Illinois (where Oak Wilt is a widespread problem) has shown that not pruning or injuring trees during the summer has really been effective at slowing the spread of Oak Wilt. Moreover, all pruning of oaks should be withheld until the dormant season in areas where Oak Wilt has been already been detected.
For more information about either disease, contact either your local MSU Extension office or the Michigan Department of Agriculture Regional office closest to you.
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