Oak wilt is a fungal vascular disease affecting all species of oak trees, killing the tree. Oak wilt spreads by root grafts with neighbouring oak trees, by sap-feeding beetles, and/or by moving infected firewood. Oaks in the red oak group (red, black and pin oaks) are highly susceptible whereas oaks in the white oak group (white, bur and swamp oaks) show some degree of resistance to infection.
Oak wilt has been detected in the City of Niagara Falls, Ontario, the Township of Springwater, Ontario, and the Town of Niagara-on-the-Lake, Ontario. These are the first confirmed detections of oak wilt in Canada. Oak wilt has not been confirmed in Toronto.
Symptoms & Impacts
Symptoms
Leaves turn dull green, yellow-bronzy colour.
Discolouration of leaves that starts from the edge of the leaf into the middle.
Early leaf fall, including green leaves, in July to August.
Vertical bark cracks in the trunk and large branches caused by the fungal mats – also referred to as pressure pads – exerting outward pressure on the bark.
Fungal mats have a sweet, fruity smell.
Photo credit: Invasive Species Centre
Similar diseases
Oak leaf anthracnose and oak leaf blister are common fungal diseases in Toronto that may be mistaken for oak wilt. Neither oak anthracnose nor oak leaf blister is considered a serious disease that will threaten the tree’s health.
hundreds of different pollinator species use oaks as a host tree to lay their eggs
caterpillars will eat oak leaves, attracting birds to nest in the trees in spring and eat the caterpillars
Oak wilt also:
Reduces tree air and water filtering
Lowers property values and creates poor neighbourhood aesthetics
Increases costs due to tree maintenance, removal and replacement
Reduces shade
What You Can Do
Do not prune oak trees during the growing season – April 1 to October 31 – to avoid attracting the sap-feeding beetles that transmit the disease. If pruning is necessary or a branch is broken, apply wound paint to the cut/broken area.
Do not move firewood to prevent the spread of infected material.
Apply good arboricultural practices to improve the general health of the trees, including watering, mulching, pruning for maintenance and preventing injury to the tree.
Report potential sightings of Oak wilt symptoms online to the CFIA.
