Oak Wilt in Wisconsin

Oaks are among our favorite trees, and probably yours too. What’s not to love? They grow to be large, beautiful, and strong, providing shade, acorns, and they are visually stunning. Oaks can live for hundreds of years and we are blessed to have some in our area that are over 300 years old.

Sadly, Oak Wilt has become somewhat prevalent among Oaks in Southern Wisconsin. What is Oak Wilt? Oak Wilt is caused by the fungus Bretziella Fagacearum. According to the Wisconsin DNR “The fungus grows through the infected tree’s water conducting system, causing the tree to wilt and die. Oak Wilt is introduced to an area by sap-feeding beetles that carry Oak Wilt spores to fresh wounds. Spore-bearing fungal mats develop under the bark in the fall or spring following the death of the infected tree.”

To identify Oak Wilt, look for leaves that fall from the upper canopy of Oaks in July and August. The leaves will look dull green or bronze and water-soaked but partially green.

One of the ways to avoid spreading Oak Wilt is to prune or cut Oaks during their dormant season. During this colder period the spore-carrying beetles are dormant and so are not able to spread the spores from one tree to another. This Oak Wilt Vectors Emergence Thermal Model created by the UW Extension can provide an idea of when cutting and pruning of Oaks should be avoided. At Tree House Arbor Science we adhere to the City of Madison Ordnance that prohibits pruning of Oaks between April 1 and October 15.

Oaks may also suffer from other issues like Burr Oak Blight, Anthracnose, Leaf Tatters, leaf and twig galls, and Two-Lined Chestnut Borer infestations. The University of Illinois has produced a helpful flyer describing these issues.

If you suspect your Oak has Oak Wilt or some other issue affecting its health, please reach out to us using the form below and we will stop by for a look to help you determine the best path forward.