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Oak Wilt

Oak Wilt is a disease that impacts all species of Oak trees. It especially affects the Red Oak group, which includes Red, Pin and Black Oaks. It is caused by a non-native fungus called Bretziella fagacearum, which restricts the flow of water and nutrients in infected trees. The disease can progress rapidly and cause trees to die within a year.

There are no known cases of Oak Wilt in Canada. However, it has been found near Windsor, Ontario, in Belle Isle, Michigan.

Why is Oak Wilt a threat?

Mississauga has over 14,000 Oak trees that provide important benefits, including slope stabilization and reduced soil erosion and pollution. They also provide habitat and food sources for many wildlife species. The loss of Oak trees from Oak Wilt would result in the loss of these benefits.

How it spreads

The fungus spreads through picnic beetles, root-to-root contact, or people moving around firewood with pests and diseases.

How to spot an infection

Oak trees with an Oak Wilt infection can be identified by:

  • Leaf discoloration and wilting
  • Early leaf drop
  • Change in the colour of leaves near the crown of the tree
  • Cracks in the bark
  • Fungus in the form of grey or tan mats found under the bark of infected or dying trees

What we are doing

To prevent a possible Oak Wilt infection, the City is not pruning Oak trees between May 1 and August 31, unless exceptional circumstances such as potential safety hazards occur. In these cases, the City is applying a protective coating to the tree’s wounds to prevent attracting beetles that spread Oak Wilt. The City is also applying protective coating to all Oak trees pruned in April, September and October.

Additionally, the City is educating City staff members, residents, and partners about Oak Wilt, detecting it early and preventing the spread.

What you can do

You can help protect Oak trees on your property and the City by:

  • Learning how to identify Oak trees and Oak Wilt.
  • Avoiding pruning Oak trees between May 1 and August 31. If you must prune your tree during this time, make sure to paint the wounds with pruning paint or any latex-based paint.
  • Not moving firewood around.
  • Being on the lookout for signs of infection on your Oak trees. When in doubt, contact a tree care company to have your trees inspected.
  • Reporting suspected Oak Wilt to Canadian Food Inspection Agency or calling 311 (or 905-615-4311 from outside Mississauga).