Oak wilt is one of the few tree problems in Michigan with a firm date on it. Get the timing right and most of the risk goes away.
The dates
The Michigan DNR's April 2024 release asks homeowners not to prune any oak trees from April 15 to July 15. In Michigan, the infection risk peaks in May and June.
How it spreads
- Beetles. Sap-feeding beetles carry spores from infected trees to fresh wounds on healthy oaks.
- Roots. Neighboring oaks can share grafted root systems, and the disease moves through them.
- Firewood. Wood from infected trees can carry it to new places.
Which oaks are most at risk
The red oak group (black, northern red and northern pin oak) is the most susceptible; their leaves have pointed tips. The white oak group (white, swamp white and bur oak) has rounded leaf edges and better resists the disease spreading through the whole tree.
Symptoms
Symptoms usually show from late June through September. The DNR says affected trees suddenly begin to wilt from the top down and drop leaves quickly, and the leaves can be green, brown or both when they fall. Oak wilt is common in the Lower Peninsula.
If an oak gets wounded during the window
Storms, mowers and construction don't wait for July. The DNR says to cover any wound on an oak between April 15 and July 15 right away with tree-wound paint or latex-based paint. Don't paint wounds on other tree species; it can slow their healing.
Wood from an oak wilt tree
Trees killed by oak wilt can be burned on site, chipped, or debarked before April 15. Firewood that has dried for more than a year, or whose bark has loosened, can no longer spread the disease.
What this means for a quote
The DNR's window is about fresh wounds on oaks, whether from a planned pruning cut or a nick while clearing around one. When you get a quote for oak trimming, ask for a date outside April 15 to July 15. See trimming and pruning.