What to Know About Oak Wilt

What is it?

Oak wilt is a fungal disease that kills oak trees. Red oaks (the ones with pointed, bristle-tipped leaves, like northern red oak, black oak, and pin oak) are hit hardest and can die within a few weeks of infection. There is no cure for an infected red oak. White oaks (rounded leaf lobes) are more resistant.

How does it spread? 

Sap-feeding beetles carry spores from infected trees to fresh wounds on healthy oaks, mostly in spring and early summer. The fungus also moves underground through roots that graft between neighboring oaks, and over long distances in infected firewood.

How to prevent it

• Don’t prune or wound oaks from April 15 to July 15. This is the high-risk period. The best time to prune is winter, when trees are dormant. Arborists book up, so schedule winter tree work in the fall.

• If an oak gets wounded in spring or summer, cover the wound right away with tree-wound paint or latex paint. Beetles can find a fresh wound within minutes.

• Be careful with mowers and string trimmers around oak trunks.

• Don’t move firewood, especially oak, and don’t bring in firewood from unknown sources.

If you have Confirmed Oak Wilt:

• Report it to the Michigan DNR using the Oak Wilt Interactive Mapping Tool, found on the DNR’s oak wilt page.

• Inform your neighbors.

• Consult a certified arborist and treat nearby trees with a fungicide to make the tree more resilient to the oak wilt fungus.

• For the infected tree, cut the root grafts to help prevent spread.

• Remove the tree when dormant.  Even though the tree appears dead, there is still live tissue.  As much of the tree should be chipped and removed. Burning the tree is also a good way to stop the fungus from spreading.  Keeping the cut wood on your property can still spread the disease, so remove the wood or keep it completely covered for at least 2 years.