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Oak Wilt

tree infected with oak wiltThe image above shows symptoms of Oak Wilt killing an oak. Photo by Steven Katovich.

Where is Oak Wilt?

Oak Wilt has never been detected in Canada before, but the disease is widespread less than 600m from Windsor, Ontario, on Belle Isle, Michigan. That’s only five football stadiums away! London is strategically located along the corridor where Oak Wilt could make its way into Ontario. Having an educated and engaged community aware of this disease that can help with early detection is especially important.

What is Oak Wilt?

Oak Wilt is an aggressive disease that affects all species of oak trees, especially red oaks. It is caused by a non-native fungus that is spread by “picnic” beetles, by root to root contact, or by people moving firewood from place to place. The fungus invades the water vessels in the sapwood of oak trees, blocks them, and kills the infected trees. Death is sudden, and it often appears that the tree is wilted (“oak wilt”).

At the advanced stage of infection, cracks and patches of white, grey or black appear on the tree emitting a characteristic fruity smell (like Juicy Fruit gum!) that attracts insects that help spread the fungus to other host trees.

Once a tree has the disease there is nothing we can do for that tree, but we can try careful root pruning (to prevent spread by roots to neighbouring oak trees), and destroy the infected tree promptly without moving it elsewhere.

















The image above shows an Oak Wilt pressure pad. Photo by Julie Holmes.


Tips to Prevent Oak Wilt

Don’t Move Firewood!
If an infected tree was cut down for firewood, it should be burned as quickly as possible, and never taken elsewhere, like to a camp or cottage! By not moving firewood, you will help prevent the spread of all sorts of pests and diseases that threaten our forests. 

Avoid routine pruning of oak trees between April and July!
This is also the time of the year that “picnic” beetles carrying the fungal spores are active and can be attracted to the sweet smelling infected Oaks. If the work is an emergency than prune branches that are only needed to make the area safe. Immediately after the wound is created, paint the area with pruning paint or even latex paint to provide a barrier to the “picnic” beetle.

Be on the lookout for unusual changes!
Give your oak tree special attention and observe it during the seasons for changes. 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. If green or browning leaves are on the ground in July and dropping early that is a common sign of Oak wilt.  

Contact an Arborist!
It’s good practice to have trees inspected yearly. An Arborist may be able to see symptoms in Oak trees that would perhaps not stand out to the homeowner.   

brown leaves

The image above shows an example of discoloration of leaves progressing from the edge of the leaf to the middle; premature leaf fall (including green leaves). Photo by Joseph O’brien, USDA Forest Service.

What is the City doing?

Oaks comprise about 1% - 2% of our urban forest, and generally there are more white oak species than red oak species in London. White oaks tend to die more slowly when infected by Oak Wilt. According to The City of London’s tree inventory, we have an estimated 8,000 oak trees, with about a 50-50 makeup of red and white oak types.

The City’s Forestry Operations are following best management practices (BMPs) such as scheduling routine non-emergency pruning of oaks outside of the months of April-July during the active period of the “picnic” beetle.

Although oaks make up a relatively small percentage of the urban forest, they are very important, usually living for centuries and growing to a large size, providing food, shelter and a place to live for hundreds of other species of native wildlife. Many of London’s older mature trees are oaks, which contribute to a diverse tree canopy cover.

How to Report Oak Wilt

By law, finding this disease, or suspecting it, must be reported to the Canadian Food Inspection Agency (CFIA). The City of London is supporting the CFIA with early detection of the disease in Canada and asks residents that have concerns with an oak tree that dies suddenly or appears to be showing signs or symptoms of oak wilt to contact the CFIA or the City's Urban Forestry division immediately.

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