Oak wilt

Oak Wilt is an aggressive disease that affects all species of oak trees, especially red oaks. A non-native fungus spread by “picnic” beetles, by root-to-root contact, or by people moving firewood from place to place causes the wilt. 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, which spreads the fungus to other trees.

Once a tree has the disease, it cannot be saved. We try careful root pruning (to prevent spread by roots to neighbouring oak trees), and destroy the infected tree promptly.

To protect against Oak Wilt

1. Don’t move firewood.

Taking firewood to a camp or cottage can spread the disease to other areas of the province.

2. Avoid routine pruning of oak trees between April and July... 

...as this is when “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.

3. Be on the lookout for unusual changes.

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.  

4. Contact an arborist.

An Arborist may be able to see symptoms in oak trees that would perhaps not stand out to the homeowner.

Last modified:Thursday, September 17, 2020