April is Oak Wilt Awareness Month!


This spring and summer, be on the lookout for Oak Wilt! This fungal pathogen can be found in 61 Michigan counties, and may kill as many as 149 million trees. Spread of oak wilt is highest between April and July, and prevention is crucial to preventing its impact.


What is Oak Wilt?

Oak Wilt is a disease caused by the fungal pathogen Bretziella fagacearum and primarily effecting red oaks. The fungus grows in the vascular tissue of infected trees, blocking water transport and causing trees to wilt and die. White Oaks may also be affected, but the impact is slower and less likely to spread to nearby trees.

Photo:t USDA Forest Service - Forest Health Protection Eastern Region,  Bugwood.org
Oak wilt spore mat and surrounding pressure point

How can I identify Oak Wilt?

Trees infected with oak wilt often have distinctive fruiting bodies called spore mats, surrounded by discolored pressure pads. These spore mats typically form in spring and summer months when conditions are damp.

 Photo: Joseph O'Brien, USDA Forest Service
Wilt pattern in oak leaves

Wilt can also be identified by the rapid loss of leaves during the summer. Fallen leaves are typically brown or partially bronzed, and will appear dried out and wilting. Wilting typically begins at the top of the tree, with affected leaves turning a paler green.


How does Oak Wilt spread?

The spore mats of infected trees give off a sweet-smell, attracting sap beetles and other insects. These insects can then spread the spores to wounded living oaks, infected cuts with the fungus. To prevent the spread of these spores, avoid damaging or wounding oak trees, especially between April and July, when these bugs are most active.


Oak wilt may also travel through root systems to infect healthy trees. This is most common in Red Oaks, which have extensive root systems connecting them to other nearby oaks.

The fungus can also travel long distances through the movement of firewood. Oak wilt spores can remain active in wood even after the tree dies, and moving firewood can spread the infection.


How can I treat infected trees?

Unfortunately, there is no treatment for infected trees. When an infected tree is confirmed, the only option is to stop the spread to nearby trees. Removing an infected tree without cutting it off from the root system will not prevent spread, and could result in healthy trees becoming infected.


How do I prevent oak wilt?

There are a few crucial steps you can take to stop the spread of Oak Wit:

  1. DO NOT prune or trim your trees between April 15 and July 15.

  2. DO NOT move firewood. It may be infected with oak wilt, and moving it could spread the fungus to healthy trees.

If you suspect a tree is infected, contact us at the Saginaw Bay CISMA at sbcisma@gmail.com, for identification, or the Department of Natural Resources Forest Health Division at DNR-FRD-Forest-Health@michigan.gov..

You can also report invasive species using the Midwest Invasive Species Information Network (MISIN) online reporting tool, or download the MISIN smartphone app and report from your phone at http://www.misin.msu.edu/tools/apps/#home

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