*Detected in Michigan*
Joseph O'Brien, USDA Forest Service - Wilt pattern in oak leaves
Bill Radtke, Michigan DNR Forest Health Program - Oak wilt mortality after firewood introduced
Why we care: Oak wilt kills healthy red oaks. White oaks can also be affected but are more resistant and less
vulnerable to mortality from the disease. Once a red oak becomes infected with the oak wilt fungus, the tree will die,
and there is no treatment to save the infected tree. Once an oak wilt infection is confirmed, however, treatments are
available to save surrounding oaks and stop the spread of this disease.
What is at risk? All red oaks are susceptible to oak wilt. Red oaks are common urban and suburban landscape trees.
The loss of these trees can have a significant negative impact. In the forest, red oaks are also an important producer of
acorns for wildlife habitat. Using 2011 Forest Inventory and Analysis data along with the current average stumpage
price for red oak sawlogs, it is estimated that the value of red oak timber in Michigan is approximately 1.6 billion
The threat: Oak wilt moves slowly on its own through root systems and travels short distances overland when new
spores are moved by beetles from an infected tree to a freshly pruned or injured tree. Oak wilt can be moved long
distances when people move infected firewood from one location to another. Look for red oaks that suddenly drop their
leaves in the summer. The disease spreads, killing nearby oaks from one year to the next. Currently, oak wilt is
generally distributed throughout the Midwest and Texas.
What could happen in Michigan? Once established, if not treated, oak wilt will continue to spread, killing all red oaks
in a neighborhood or a forest.
What can you do? DO NOT prune oak trees during the growing season. If you need to prune oaks, DO NOT prune
them between April 15 and July 15. DO NOT move firewood: oak wilt is spread by the movement of infected wood.