Oak trees have a reputation for being mighty, but if these majestic trees are pruned or wounded from early spring to early summer, they are susceptible to the spread of a microscopic killer.
From April 15th to July 15th, oak trees are at high risk for oak wilt, a serious fungal disease that can weaken white oaks and kill red oak trees within weeks of infection. During this time of year, flying beetles can carry oak wilt fungus spores from tree to tree and the fungus can infect trees through wounds left by pruning or storm damage.
The fungus can move from an infected oak to neighboring oaks through root grafts. Depending on tree size, adjacent oaks may be connected to other trees, or grafted, through root systems. Roots of large trees can reach 100 or more feet. Left untreated, oak wilt will continue to move from tree to tree, killing more oak over an increasingly larger area. As more trees die from oak wilt, more fungal spores are produced, which allows the beetle to carry infection to new locations.
Symptoms most often appear from late June through September. Affected trees will suddenly begin to wilt from the top down, rapidly dropping leaves, which can be green, brown or a combination of both colors.
If you have a tree that gets damaged during the risk period from April 15th to July 15th, immediately cover all wounds with tree-wound paint or latex-based paint.
If you suspect oak wilt:
- Report infections at Michigan.gov/ForestHealth using an interactive map.
- Contact a local DNR forest health specialist for more information at 517-284-5866.
- Seek verification from Michigan State University. Find instructions at canr.msu.edu/pestid or call 517-355-4536.
- Get help from an oak-wilt qualified specialist. Visit MichiganOakWilt.org for a listing and more information.