By Linda Williams, DNR Forest Health Specialist, Woodruff, Linda.Williams@wisconsin.gov or 920-360-0665. 

Symptoms of oak wilt are showing up. Look for leaves that suddenly wilt and drop from the tree. Oak wilt is a non-curable, fungal disease specific to oaks. Trees in the red oak family will die quickly from this disease, while trees in the white oak family will die more slowly, with a branch or portion of the crown becoming infected. 

This tree is actively wilting from oak wilt infection and will drop most of its leaves within about 4-6 weeks.

Trees infected this year with the oak wilt fungus are currently turning off-color, dropping their leaves and will soon be dead. Leaves that drop to the ground are often still partially green, close to the petiole.  Once a tree is killed by oak wilt, the fungus will move down into the root system and begin to spread outward from the roots of the infected tree through root grafts into the roots of neighboring trees. In this way, over several years, a pocket of dead oaks will be created and the disease will continue to spread through the roots unless something is done to break the root grafts. Or it will stop when the disease runs out of oaks in that area.

Check out the Wisconsin DNR oak wilt webpage to read the forestry guidelines on how to reduce the risk of new overland infections as well as control options for existing oak wilt infections. Another resource is this University of Wisconsin-Extension brochure about oak wilt, which includes the biology of the disease and how it spreads.

Leaves that drop from infected trees are often still green near the base of the leaf while the remainder of the leaf may be brown or appear water soaked.