Imagine Canatara Park without Oak trees.
Right on the heels of the wipeout of Ash trees due to the Emerald Ash Borer is a similar threat to our precious Oak trees by Oak Wilt. And while we know that Oak Wilt (Ceratocystis fagacearum) has not yet crossed the border into Ontario, experts believe that it is just a matter of time.
Oak Wilt has already impacted over 20 states including nearby Michigan, Ohio, Indiana and Illinois.
Oak Wilt is a rather complicated fungus that restricts the flow of nutrients and water at the outer sapwood of the tree. In other words, xylem, or pipes that transport water and nutrients from the roots to the branches become plugged up, causing leaves to wilt. Once affected, death of the tree can occur as quickly as within one growing season.
To make matters difficult, Oak Wilt relies on certain bark beetles to spread Oak Wilt from place to place and from tree to tree, and will do so primarily in May and June. The beetles need open tree wounds and fresh cuts as entry points to spread the fungus. We already know that avoiding pruning Oaks will reduce the rapid spread of Oak Wilt.
Unfortunately, the fungus can also be spread from tree to tree through root grafts, which naturally form as roots grow. Root grafts form when roots from different trees criss-cross and become welded together.
At this stage it is difficult to predict the level of devastation that Oak Wilt might have. Our own City of Sarnia Parks staff has recognised the fungus as a serious threat and have recently attended seminars in Michigan to learn more details. The Canadian Food and Inspection Agency has devoted significant study to the issue and has already written documents to assist and inform the Canadian public.
No doubt experts will soon disseminate more information to educate us about methods to mitigate the threat of Oak Wilt. According to the Canadian Food and Inspection Agency, the Red Oak group (generally Oaks with pointed leaves) is more susceptible than the White Oak group (Oaks with rounded leaves). Studies in the USA have found that affected White Oaks may even recover from infestation if conditions are favourable.
At this point, there is no need or benefit for us in Lambton County to hit the panic button. We would be wise to know the symptoms of Oak Wilt, which begin with wilting and browning of leaves highest in the tree. Once affected, symptoms move to the centre of the tree. Less conspicuous symptoms include greyish fungal growth resembling blisters or warts developing under the trees’ bark.
There is no known quick fix or cure for Oak Wilt. We would be wise to avoid the movement of Oak firewood, particularly between USA and Canada. If and when Oak Wilt arrives in Ontario, we should avoid pruning, cutting and harvesting Oaks in May and June. Trees that have been damaged exposing fresh wounds should be protected by applying a sealing compound to cover beetle entry points.