Species Name: Oak Wilt (Ceratocystis fagacearum)
Description: A fungal disease occurring in oaks. Once an oak tree is infected, the fungus moves through the vascular system of the tree, preventing the uptake of water and nutrients. Leaves will wilt rapidly, starting at the tips of the leaves in the upper-most branches, moving downwards. Infected trees may develop a mat of fungus under the bark that causes the bark to break apart. The fungus can spread through beetles, roots, and by human disturbance. Both red and white oaks are susceptible though white oaks have tyloses, essentially extra cellular structures that provide some natural resistance.
Similar species: Oaks may also suffer from Anthracnose, another fungal disease that causes symptoms in the leaf. In years of drought, oaks may experience other fungal diseases such as Armillaria (Armillaria mellea). The Two-Lined Chestnut Borer (Agrilus bilineatus) can cause similar symptoms in oak. Oak Wilt is generally fast moving, and lethal. Killed trees may exhibit fungal mats under the bark.
Origin: Unknown; it was first discovered in Wisconsin in the 1940s.
How it spreads: The Oak Wilt fungus can be transmitted from infected trees through root systems. Beetles can be attracted to dying and dead infected oaks and spread the disease to healthy trees. Human activity can also spread the fungus, and impact healthy oak trees. For example, pruning trees in the summer when the fungus is actively fruiting can infect new trees. Retaining or transporting wood from infected trees allows contributes to the spread of the disease.
Extent in Michigan: Oak Wilt is present in both the Upper and Lower Peninsula. In the Upper Peninsula, Oak Wilt is present in the southern central counties, but all counties are at risk.
Why is Oak Wilt a problem: An infection of Oak Wilt is lethal to an oak tree and likely a death sentence to any oak trees in the nearby vicinity. Oaks are relatively slow-growing and hard to establish; oaks provide an excellent food source for wildlife. Many urban and yard trees are some type of oak. Treatment options for oak wilt are severe as it is hard to control the fungus and an infected tree is a risk to healthy trees.
Management actions/options: For single, healthy trees, injections of fungicide can be used as a prevention tool. In infected trees and woodlots, removal of dead trees and root plowing may be an option for protecting uninfected trees. Pruning of oak should be limited to winter months. Do not move firewood. More research is being done to find the best way to minimize the impacts of Oak Wilt in forests. Before taking any action, confirm that it is Oak Wilt infection. If you suspect Oak Wilt, report it!
REPORT IT: Email the Michigan DNR at DNR-FRD-Forest-Health@michigan.gov or call 517-284-5895
Links and References:
Michigan DNR: http://www.michigan.gov/dnr/0,4570,7-153-10366_54559_10402-381392--,00.html
University of Minnesota Ext.: http://www.extension.umn.edu/environment/trees-woodlands/oak-wilt-in-minnesota/