Oak Wilt – April 7, 2018

Garden Clippings

“On Canada’s doorstep.”

Those are the words Phillip Kurzeja used when he spoke to the audience at the March 28 information session discussing Oak Wilt.  The education event was put on by the City of Sarnia and was geared to arborists, nursery workers, tree enthusiasts and those in the tree removal business.

Kurzeja, with the Michigan Department of Natural Resources was accompanied by Richard Wilson of the Ontario Ministry of natural Resources.  Together, they spent two hours feeding a captive audience on the science of the problem and what we can do to minimize the impact of Oak Wilt.

Citizens of Sarnia Lambton and across Southwestern Ontario know all too well what it means to lose an entire tree species.  The Emerald Ash Borer began its destruction in 2002 and within a decade every Ash tree was dead or dying.

“Oak Wilt does not behave like Emerald Ash Borer” Wilson explained.  “Where the Ash Borer rapidly killed all Ash trees, Oak Wilt behaves a little more like Dutch Elm disease.  We’re not likely to see a widespread disappearance of all Oak trees.”

Oak Wilt is a highly effective exotic fungal pathogen that can attack an Oak tree and doom it within days.  But the pathogen needs a sap beetle (nitidulid) to move and spread the fungal spores from infected trees to healthy trees.  The beetles need an open wound or fresh cut to obtain a point of entry into a new Oak tree.

The other way Oak Wilt can spread from tree to tree is via root grafts which are roots of two trees that have grown together and are sharing the same tissue.   Isolated trees that are not near other Oaks are therefore safer than those in a crowded bush.

Wilson and Kurzeja emphasised the importance of not pruning Oak trees anytime between just prior to leaf flush and after leaves are fully developed.  It is during this two-month period that the nitidulid beetle is active and will spread spores.  To be on the safe side, Oak trees should not be pruned during the months of April, May, June and July.

Oak trees within the Red Oak group appear to be more susceptible than those that fall within the White Oak group.  Damage is quicker for Red Oaks and symptoms are easier to detect.  For Red Oaks, the period between attack and death can be a matter of months, while White Oaks might take a few years to die.

The two Oak tree groups are easy to distinguish from one another.  Red Oaks have leaves with pointed ends, while White Oaks have rounded leaf ends.  Examples of Red oaks are Scarlet, Pin, Northern Red and Black Oaks.  Within the White Oak group is included Burr Oak which is so prevalent in Southwestern Ontario.

Next week’s garden Clippings will look at practical ways we can minimize the damage of Oak Wilt.