OAK WILT: SPOT IT AND STOP IT

July 23, 2026
Oak Wilt

Oak Wilt is an invasive fungus (Bretziella fagacearum) that restricts water and nutrient flow through Oak Trees causing leaves to wilt, eventually leading to tree death. It spreads above ground by sap beetles carrying fungal spores from infected to healthy trees and below ground through root systems that connect healthy trees to infected ones.  

Oak Wilt can cause permanent and costly damage to Oak Trees in the York Regional Forest, in parks, on our streets and on your property. While Oak Wilt has not yet been reported in York Region, knowing the signs and symptoms and reporting suspected finds can help prevent its introduction and spread. 

Oak Wilt signs:

  • Wilting and dull-green, brown or yellow leaves
  • Leaves changing colour throughout the spring or summer starting at the leaf tip and moving in towards the centre and then down towards the stem
  • A carpet of leaves under the tree mid-summer; Oak Trees typically don’t drop their leaves until late fall/early winter  
  • Cracks in the trunk and/or white, grey or black fungus under the bark of dead trees; fungus will appear approximately 10 months after the tree has died  

To help stop the spread:

  • Check your trees regularly for signs of Oak Wilt and report suspected finds to the Canadian Food Inspection Agency by emailing @email or calling 647-790-1100
  • Do not move branches or firewood as you could accidentally spread Oak Wilt to areas not yet infected
  • Do not prune Oak Trees between April and November - this reduces the risk of attracting sap beetles  
  • When pruning Oak Trees, always sanitize tools before and after to prevent potential transfer of fungus

Oak Wilt facts:

  • Oat Wilt’s origin is unknown but it is believed to have been present in North America since the early 1900s
  • Oak Wilt was first detected in Ontario in 2023; to date, it has been found in the City of Niagara Falls, Town of Niagara on-the-Lake and Township of Springwater in Simcoe County
  • Oak Wilt has a devastating ability to infect and kill Oak Trees in as little as a few months
  • Oak Wilt does not directly affect human or animal health
  • There is currently no treatment for Oak Wilt once a tree is infected  
  • Oak Trees are native to North America and keep forests healthy; they prevent erosion, improve soil quality, protect groundwater and are an important source of food and habitat for wildlife  
  • Indigenous communities use acorns for food, for example ‘Bagaanak’ bread, known as bannock, is made using flour from dried and crushed acorns or ‘Bagaan’, and many Oak Trees hold cultural significance as symbols of heritage or landmarks; for the Anishinaabe culture, Oak Trees represent teachings of humility  
  • Oak Trees are found on a wide range of soils and sites and have a life span between 100 to 300 years; leaves are dark green on top and gray-green on the bottom
  • Over 27,000 Oak Trees are found in 15 of 24 (22 are open to the public) York Regional Forest tracts
  • York Region is monitoring the York Regional Forest and street trees on Regional roads for signs of Oak Wilt and encouraging partners including local cities and towns and conservation authorities to monitor Oak Trees on their respective properties  

Additional information

For more information about Oak Wilt including what to look for, impacts and how you can help stop the spread visit york.ca/InvasiveSpecies