Oak Wilt 3

Garden Clippings for Feb 2, 2019

This, the third Garden Clippings dealing with Oak wilt, will explore the signs and symptoms of the fungus.

We know that Oak Wilt is already doing damage in all States bordering Ontario, including Michigan, Ohio, New York, and we can conclude that despite our best efforts, Oak Wilt will no doubt enter Ontario.  Some say the fungus has already crossed the border.

Oak Wilt is difficult to detect.  First signs are mature leaves turning slightly duller in colour.  Leaves will begin to curl, lose their bright green colour and will soon turn brown or yellow, almost as if October has come early.

As the disease progresses, outer sections of the leaf become discoloured.  The yellow or brown discolouration begins at the outer perimeters of the leaf, moving towards the central main leaf veins.  The problem is most evident at the ends of the limbs and top of the tree.

Oak Wilt is easily confused with Anthracnose of Oak, another fungus that is particularly prevalent in rainy seasons.  Anthracnose, found throughout Ontario, is not deadly and does not pose a serious threat to Oaks.  Anthracnose will exhibit the same symptoms on leaves as Oak Wilt, but the former generally damages the inner leaves while Oak Wilt affects the leaves furthest away from the main trunk.

As Oak Wilt progresses, fungal growth begins to develop in the layer of heartwood just under the bark.  So strong is this fungal growth that it begins to force vertical cracks to appear on the outer bark.  But because Oaks have rough bark, these cracks or expansions are difficult to detect. A fruity smell accompanies the cracks and blisters that appear on outer bark.

Red Oaks, (pointed leaves), once infected can die within one growing season.  Oaks within the White Oak Group are more resistant and may succumb 3 years after first infected.

There is no need to push the panic button yet in Lambton County.  It is of utmost importance that we do not move Oak firewood in or out of Lambton County.  Secondly, we must be careful not to cut, prune, damage or chop down any Oaks between the 4-month period from April to July, when nitidulid beetles might spread the fungus from tree to tree.

Property owners who suspect trees on their property might be infected with Oak Wilt are obligated to contact the authorities who will follow up.  For Lambton County, contact the St Clair Region Conservation Authority in Strathroy.

The most obvious impact of the potential loss of Oak trees in Lambton County is aesthetics.  We simply love our Oak trees.  Now that Ash trees are gone, Oaks are the dominant tree in many woodlots.  The Lake Huron Shoreline, beginning at Canatara Park and extending along the lake through Pinery Park and up to Tobermory is anchored with Oaks.

Other resulting impacts include the loss of habitat for birds and other forest animals who depend on Oaks for food and shelter.  Oak trees provide valuable shade and can be a source of lumber for the forestry industry.

We know Oak Wilt is going to be a serious threat in Ontario.  And judging by the way Oak Wilt is behaving south of the border, we can guess the fungus will not quickly wipe out every Oak as was the case with Ash trees.  Next week’s Garden Clippings will examine the actions we can take to minimize the potential impact.