Oak Wilt

Oak wilt is a disease caused by the fungus Bretziella fagacearum. Oak wilt affects all species of oak trees. Red oaks are particularly susceptible, resulting in tree death within a single season. Oak trees belonging to the white oak family (white oak, bur oak, English oak) can live with the infection for decades. Oak wilt is spread naturally through root grafts or beetles carrying fungal spores. Oak wilt does not affect human or animal health.

Identifying Oak Wilt

The fungus that causes oak wilt grows on the outer sapwood and restricts the flow of water and nutrients through oak trees. The most noticeable sign of oak wilt will be a sudden wilting and premature dropping of leaves. Other signs include:

Dull green, brown or yellow leaves
Premature foliage discolouration starting from the outside margins of the leaf
Early and sudden leaf drop beginning at the crown of the tree
Development of fungal mats appearing on the trunk or larger branches that:
- appear in the spring after a tree is infected
- create vertical cracks in the tree due to the outwards pressure of the mats
- produce a sweet smell described as being identical to Juicy Fruit™ gum
- is white, grey or black in colour under the bark surface

Oak wilt leaves Oak wilt fungus

Reporting Oak Wilt

If an oak tree dies suddenly or appears to be showing signs of oak wilt, the Township requests that residents submit a report to the Canadian Food Inspection Agency (CFIA). Early detection of Oak Wilt in Canada will help reduce the spread of the disease.

Report Oak Wilt

Causes of Oak Wilt

Oak wilt can be spread in different ways:

contact with native sap feeding beetles (also known as Nitidulidae) as they move from tree to tree to feed
by moving firewood from infected oak trees
by grafted root systems below ground between nearby infected and uninfected trees

Preventing Oak Wilt

We can all help with prevention and early detection of this devastating disease.

Do Not Move Firewood

The oak wilt fungus can stay alive on cut firewood for up to one year. If an infected tree was cut down for firewood, it should be burned or disposed of by a qualified professional as quickly as possible. Taking firewood to a camp or cottage can spread many different pests and diseases to other areas of the province.

Avoid Pruning

Between the months of April and July, sap beetles are active and attracted to the sweet-smelling fungal mats located under the bark of infected oaks. The beetles can carry the fungal spores to oak trees that have open wounds from pruning cuts. If pruning is required for safety reasons, immediately after the pruning wound is created, paint the area with pruning paint or latex paint to create a barrier.

Observe Unusual Changes

Give your oak tree special attention and observe any changes during each season. Does it look like it is suffering from drought when there is not one? Oak trees should have their leaves in the spring and summer months. Leaves on the ground in July that are green or browning and/or leaves that drop early is a common sign of oak wilt.

Contact an Arborist

It is a good practice to have your trees inspected yearly. An arborist may be able to see signs in oak trees that a homeowner may not.

The Invasive Species Centre

The Invasive Species Centre prevents the introduction and spread of high-risk invasive species in Canada by connecting stakeholders with knowledge and technology.

The Invasive Species Centre’s Oak Wilt Wire is a bi-annual digital newsletter focused solely on oak wilt news. This newsletter will highlight oak wilt in the news, interesting new research, new developments in prevention and management, community oak wilt champions, and updates from oak wilt experts. Tips and trivia are also included to keep you sharp on oak wilt knowledge! If you consider yourself an oak wilt champion in your community and would like your work to be highlighted, please email the Invasive Species Centre and share your stories!

Want to learn more about oak wilt? Check out the ISC’s Invasive Species Training Program and enroll in Oak Wilt Training. This course provides participants with the knowledge and tools to identify, prevent, report, and manage oak wilt in their community and workplace.

The Invasive Species Centre held an Oak Wilt Question and Answer Expert Panel Webinar.

Watch the webinar Assessing the Risk of Oak Wilt in Canada.