Report suspected oak wilt signs to the Canadian Food Inspection Agency (CFIA).

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.


  • 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.
Vertical crack in the bark of an oak tree, indicating the possible presence of a fungal mat underneath the bark and pushing it outwards.
Photo credit: Invasive Species Centre
Bark at the location of a pressure pad (vertical crack) has been cut away to show the grey-black fungal mat underneath.
Oak leaves discoloured by oak wilt.

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.

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Oak trees are an important habitat for wildlife:

  • many birds and mammals eat their acorns
  • 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
  • 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.
  • Mapping, evaluating and monitoring susceptible oak trees and oak stands.
  • Implementing pruning restrictions for staff and contractors 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.