Oak wilt is an extremely devastating and costly disease. It is an exotic, invasive and lethal disease of oak trees. It creeps from the top down, blocking the tree’s vascular system (tubing used to collect food and water), dropping leaves either entirely green or green and brown with a distinct line dividing the dead and living tissue. If red oaks become infected, they may die in as little as three weeks. White oaks are more resistant so the disease progresses more slowly.
For some time now, this vascular disease has been spread across Michigan by way of a tiny black picnic beetle that transmit the spores. The sap beetles are attracted to injured oaks trees by the fruity smell of the tree’s sap that runs from open wounds. The spores then enter the wounds which can be caused by tree-climbing spikes, pruning, nailing signs on trees and accidental tree-barking (a wound created when bark is removed by impact from equipment like mowers or string trimmers). Once an oak is infected, the fungus will move underground to neighboring oaks through root grafts. Oaks within 100 feet of each other have connected or grafted root systems. If left untreated, oak wilt will continue to move from tree to tree. Adjacent oak trees can be protected and the spread of disease controlled when oak wilt is confirmed at the site and proper measures are taken.
The first line of defense is to not injure or prune oak trees in the prime time of oak wilt transmission, April – July. Insects, disease and Mother Nature do not read calendars, so always use good pruning methods. It is okay to prune when oak trees are dormant, often November through March. It is also important not to move any firewood that may be from oak wilt-killed trees during this time. When firewood is moved to a new location, any wounded oaks in that area can be infected with oak wilt. The beetles will move the spores from the diseased firewood to the wounds of the otherwise healthy oaks.
Read more from the DNR: DNR advises caution to prevent spread of oak wilt disease