April 15 to July 15 is a crucial time each year for the survival of oaks (the genus Quercus). During this window, beetles can carry spores of the deadly oak wilt fungus (Ceratocystis fagacearum) to open wounds on oak trees. Once infected oak trees can die in a matter of weeks. Unfortunately, the disease can spread from an infected tree to nearby oak trees because their roots are commonly grafted together underground. Home construction in oak woods during the spring is a common way that oak trees are wounded and infected by oak wilt.
Keep your oak trees healthy: DON’T WOUND OR CUT ANY OAKS FROM APRIL 15 TO JULY 15. If a tree is accidentally wounded, cover the wound immediately with tree wound paint or a latex paint to help keep the beetles away.
The red oak group is very susceptible to oak wilt. In Michigan, this group includes Northern Red Oak (Quercus rubra), Black Oak (Quercus velutina ) and Pin Oak (Quercus palustris). The red oak group is easily recognized by the prominent bristle-tips on the lobes of the leaves. The other group of oaks in Michigan, the white oaks, do not have bristle-tips on the lobes of their leaves. The white oak group includes the common species White Oak (Quercus alba), Burr Oak (Quercus macrocarpa), and Swamp White Oak (Quercus bicolor). White oaks can be infected by oak wilt but generally are not as susceptible to this fungus. White oaks may die over one to several years if infected with oak wilt.
If you’re not sure which you have, a general rule of thumb is that members of the red oak group have bristle-tips on the lobes of the leaves whereas white oaks have lobed edges without points, a more rounded look. Here are 1) the Northern Red Oak’s bristle-tipped leaves in the spring; a Burr Oak (part of the White Oak group) with leaf tips that lack bristles and long catkin of flowers; and a White Oak in the autumn with its rounded lobes that lack bristles at the tip. Here’s a Michigan DNR link with some drawings to help you out, too.
Another reminder: DON’T WOUND OR CUT ANY OAKS FROM APRIL 15 TO JULY 15. If an oak tree on your property dies of oak wilt, the firewood should be immediately covered with plastic and sealed to the ground with stones or other weights until the following August in order to 1) keep the beetles away and 2) generate enough heat inside the plastic to kill the fungus. And don’t transport any infested oak firewood to another area, thereby transporting the fungus as well.
We’re called Oakland Township because we are surrounded by these beautiful giants of the plant world. Please remind yourself and your neighbors not to prune or wound oak trees between April 15 and July 15, so we can preserve the beauty of our very special area.
For more information about Oak Wilt, check out these links from the Michigan DNR:
- DNR Advises Caution to Prevent the Spread of Oak Wilt Disease
- Forest Pest Alert: Oak Wilt
- How to Identify, Prevent, and Control Oak Wilt
- Oak Wilt in Michigan