Oak Wilt

Cause

Oak Wilt is caused by a fungal invasion of an oak tree’s water conducting vessels. When a tree detects the fungus, it responds by plugging it’s vessels to keep the fungus contained, but the fungus remains ahead of the tree and essentially the tree causes its own death by cutting off the water supply. Oak wilt can be spread through direct contact from a beetle carrying the fungus to an open wound or through roots that have grown together between two or more trees. Oak wilt infects the majority of trees through grafted roots. Oak wilt is exclusive to oak trees and does not pose any risk to other tree species. 

Red oak trees (red and pin oak) are highly susceptible to oak wilt and often die within a few weeks of the first visible symptoms. Oak wilt is first observed as wilting leaves in the upper crown followed by premature leaf fall. Leaf wilting and falling escalates throughout the crown as the disease progresses downward into the root system. Fallen leaves typically appear brown along the edges and inward while major lateral veins and the mid-vein remain green. Once symptoms appear, there is no effective treatment to prevent death. Oak wilt typically spreads into nearby red oaks through grafted roots. Root graft barriers and fungicide injections are recommended preventive practices against oak wilt. Diseased red oak wood must be processed through a wood chipper, properly covered in heavy plastic, or treated in another effective manner to control oak wilt spore pads. 

White Oaks

White oaks (bur, white, and swamp white oak) are somewhat resistant, usually wilt much slower, and may not die for many years. The wilting leaves may be more random and scattered throughout the crown from year to year. White oaks can live with the disease sometimes for years and may be treated successfully with fungicides. Diseased white oak wood does not produce oak wilt spore pads and can be used safely without any treatment.  View more information on oak wilt in Minnesota.