Background

Oak wilt is a fungal pathogen (Bretziella fagacearum) killing thousands of oak trees in North American forests and woodlands each year. The fungus is able to spread from infected to healthy trees by underground roots and two groups of insects; the sap and bark feeding beetles.

Oak wilt is highly susceptible in all species of red oak species, including the northern red oak (Quercus rubra), northern pin oak (Quercus ellipoidalis), and the Spanish oak (Quercus falcata). Fungal mats found on infected trees are transferred to the beetles bodies while feeding and then carried to other trees.

Range

Oak wilt has been reported throughout the northwestern United States, along the Great Lakes region and southwest as far as Texas. Found in Canada for the first time in 2023, in the Niagara Falls area of Southern Ontario, it has now also been confirmed in the Township of Springwater, near Barrie, and in Niagara on the Lake. The Canadian Food Inspection Agency regulates the importation of oak materials.

Impacts of Oak Wilt

• Once a tree is infected, the disease can progress rapidly, with some trees dying within a year.
• Eliminates oak tree populations that have ecological importance for stabilizing slopes, limiting soil erosion and reducing air pollution.
• Acorns from oak trees are a valuable commodity for wildlife species.
• Tree mortality decreased economic values of oak tree products.

How to Identify Oak Wilt

• Red oak leaf discoloration and wilting occurs very fast.
• Leaves begin to change color near the upper portion of the tree crown and as the disease progresses, turn bronze in color.
• White oaks react slowly to the disease compared to red oaks, usually dying one branch at a time. The discoloration and wilting of leaves in white oaks is similar to red oaks.
• Fungus is found beneath the bark of infected or dying trees in the form of gray or tan mats.

Each case of oak wilt is different and symptoms among trees are variable and not always visible.

What You Can Do

• Learn how to properly identify the signs and symptoms of oak wilt
• If you’ve seen signs of oak wilt or any other invasive species in the wild, please contact the toll-free Invading Species Hotline at 1-800-563-7711, visit EDDMapS to report a sighting.

Resource Files

Other Resources

• Invasive Species: A Threat to Ontario’s Biodiversity
• Invasive Species Centre

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