Be aware of oak wilt

City Tree Commission warns of deadly fungal tree disease

TIFFIN, OHIO – October 15, 2021 – City of Tiffin Tree Commission members are urging the public to be aware of oak wilt, a deadly fungal disease that is widespread in Ohio and has been reported in nearly every county. Oak Wilt can affect any oak species with red oaks (black, pin, red, scarlet, shingle oak, etc.) being far more susceptible than white oaks (bur, chinkapin, swamp white, white oak, etc.). Once a tree has become infected there are no proven methods for saving the tree.

Early signs of oak wilt can include the withering of leaves in the upper canopy of affected trees. This can be very pronounced in red oak species as the leaves often will often turn yellow or brown along the outsides of the leaf, with the veins remaining green for a while longer. White oaks may not change as drastically. Late spring infections will typically result in wilting during mid-summer in red oaks. Infected dead or dying red oaks can also be identified by the appearance of fungal mats that grow beneath the bark and create spores and can cause the bark to crack and break open.

Oak wilt symptoms can often closely resemble other factors, such as drought, or diseases like leaf anthracnose. The only way to identify oak wilt with certainty is to have samples of the tree tested by a specialized laboratory, such as The Ohio State University C. Wayne Ellett Plant and Pest Diagnostic Clinic.

Text Box: This pictures shows the leaves of a red oak tree affected by oak wilt.Oak wilt can spread over and underground. Underground is by far the most common as infected trees will spread the disease to neighboring trees through root grafts. This can only happen between the individual group of oaks (red oaks or white oaks). A red oak tree cannot infect a white oak via root grafts. Over ground, the disease can spread by tiny beetles that will pick up the fungus from an infected tree. It is estimated that 90 percent of infections are transmitted through the roots, however, this method can only move to neighboring trees of similar species. Over ground transmission can occur at a long distance and does not matter which species are involved.

There are a few ways we can prevent or limit transmission of oak wilt. If infected trees are identified and there are trees of a similar species around them, then root grafts must be severed. This can be done with heavy equipment that cuts through the soil, although this method is expensive. Unfortunately, the inexpensive way is to kill the roots of infected trees and all trees within certain radius around that infected tree using herbicide. All infected trees should be removed and stored or disposed of safely. There is currently no evidence that wood chips, or firewood with the bark removed can transmit the disease.

Healthy trees without infected trees neighboring them will be fine as long as they are not subject to damage during the growing season. It is suggested not to prune oak trees anytime between April 15 and Oct. 1. If damage does occur it is recommended that wounds are dressed with a latex paint. This will slow the healing process of the tree, but will prevent beetles from transmitting the fungus through open wounds.

For more information, contact Ohio State University Extension and/or ODNR Division of Forestry.