Fungus threatens 'giant, majestic' oak trees, as disease spreads in Mich.

Windsor's majestic oaks could be at risk of a spreading fungus that has already killed dozens of trees across the border. Oak wilt appeared on Belle Isle in Detroit two years ago, and has killed more than 100 trees there already. Windsor's arborist talks about how to detect the disease.

More than 100 oaks have succumbed to the disease on Belle Isle

Oak leaves on a healthy tree. (Shutterstock)

Windsor's majestic oak trees could be at risk of a spreading fungus that has already killed dozens across the border.

Oak wilt appeared on Belle Isle in Detroit two years ago, and has killed more than 100 trees there already. 

Windsor's manager of forestry and natural areas, Paul Giroux, has been to the Michigan state park to check out the damage.

"It was a little bit overwhelming, especially when you look over your shoulder and you see Windsor only a stone's throw away," he said. "There's nothing better than actually going into the woodlot and to see the trees in decline yourself to really gain an appreciation for what a vascular wilt disease can do to giant, majestic trees."

Oak wilt has been present in Michigan for decades, said Giroux, adding that nobody is surprised to see it's getting closer to Windsor.

What to look for

It might not always be easy to spot, explained Giroux, but people should look for any sort of oak decline — like rapid leaf wilting, colour change or bark discolouration.

"Chances are if you did see something on your oak tree it's likely not oak wilt, but it's a great chance to bring out a certified arborist so that person can have a look," said Giroux. 

Early detection is important so the tree can be contained before contaminating others, said Giroux.

Oak wilt disease was discovered in Belle Isle in 2016. it's estimated to have killed as many as 112 trees so far. (Michigan Department of Natural Resources)

How it spreads

The fungus can spread from tree to tree through underground root connections, or grafts. Spores can also be spread by beetles attracted to the fungus' smell.

"The bigger threat and the more likely threat is the picnic beetle," said Giroux. "If that beetle found an oak tree that was already wounded and that beetle rummaged around in that wound, he could be spreading the spores."

Protecting trees

Giroux said there are three simple steps to protect the region's oak trees.

  1. Avoid pruning oak trees in the growing season, as it increases the likelihood a picnic beetle carrying the fungal spores will be attracted to them. If a tree does need to be pruned, treat the cut area with a latex paint to mask the scent of the tree from the beetles.
  2. Do not move firewood from one area to another. Firewood can harbour disease and fungi.
  3. Be on the lookout for unusual changes. Oak trees should have their leaves in July, and if leaves are on the ground in July that's a very common sign of Oak wilt.
The 700 year-old white oak tree in south London served as a stop during the mid-1800s for thousands of asylum seekers to congregate for safety via the Underground Railroad

The City of Windsor will step up efforts this year to alert the public to the fungal disease by doing more training of its forestry staff, as well as people who work for utilities and tree service companies.

The public is also asked to report any sick-looking oak trees to the city, the Ministry of Natural Resources and Forestry or the Canadian Food Inspection Agency.