Oak wilt (Bretziella fagacearum) is a fungal disease that affects all species of oak (Quercus spp) tree. This disease will kill the infected tree. Oak wilt spreads by root-to-root contact with neighbouring oak trees, by beetles attracted to wounds or fresh pruning cuts, and by moving infected firewood. Oaks in the red oak group (e.g. red, black and pin oaks) are highly susceptible, while oaks in the white oak group (e.g. white oaks, bur oaks, swamp oaks) show some resistance to infection. For photos and more information, click here.
Symptoms
- leaves turn yellow-bronzy colour
- leaves drop early in the season (July to August)
- cracks in the bark
- white, grey or black fungal mats under the bark
- sweet fruity smell from fungal mats
Oak wilt was confirmed in Niagara Falls, Ontario, on June 12, 2023 and in the Township of Springwater, Ontario, on June 23, 2023. These were the first confirmed detections of oak wilt in Canada. Oak wilt has not been confirmed in Toronto, and early detection is critical to reduce the impacts of this disease.
Slowing the spread:
- Do not prune oak trees during the growing season (April 1 to October 31). If you must prune during this time or if a branch is broken, apply wound paint to the cut area. These steps reduce the spread of the disease by contaminated beetles who are attracted to the fresh wounds.
- Do not move firewood. This prevents the accidental spread of infected material.
- Apply proper tree care practices to improve general tree health (including watering, mulching, informed pruning, and preventing injury).
- Report potential sightings of oak wilt symptoms to the Canadian Food Inspection Agency.
What the City of Toronto is doing:
- Mapping and monitoring susceptible oak trees and oak-dominated forest patches.
- Restricting pruning on all City-owned oak trees from April to October.
- Coordinating an oak wilt management plan along with federal and provincial agencies and municipal forestry organizations.
