Meet the latest threat to Ontario's forests — and it's lurking just off shore

It's quiet, it's deadly, and it's half a kilometre from the Canadian border.

Like emerald ash borer, or Dutch elm disease, oak wilt can kill every oak tree in its path, forester says

Oak wilt has been found in Belle Isle, Mich., about 500 metres from the Canadian border. (Shutterstock)

It's quiet, it's deadly, and it's half a kilometre from the Canadian border. And to hear forestry experts tell it, it's a dire threat to Ontario's oak trees.

Oak wilt has been found in Belle Isle, Mich., about 500 metres from the Canadian border. It can infect and kill off every species of oak, says Richard Wilson, a recently retired forest program pathologist with the Ontario Ministry of Natural Resources.

And no one really knows how to stop it.

"We all should be worried about oak wilt," Wilson said. "It's an invasive fungal pathogen very similar to the Dutch elm disease, beech bark disease, and white pine blister rust.

"These are all invasive species that have come into Canada — and Ontario especially — and have done widespread damage."

Municipalities such as Hamilton, London, and Windsor are already alerting residents to be on the lookout for oak wilt. 

"You can imagine if you don't get water to a plant or a tree for a number of days and weeks, it quite quickly can die," Sarah Rang of the Invasive Species Centre told CBC Sudbury last year. "So that's really what Oak Wilt does –  it attacks a tree like all the different species of oak, and it can cause rapid decline and even death of oak trees."

CBC News asked Wilson how to spot oak wilt, and what's at stake if it makes it to Canada.

The following has been lightly edited for length.

How does oak wilt spread?

It spreads by two ways: over land by an insect vector, a sap beetle that's attracted to oak trees that have damage wounds on them, and it also spreads underground through root systems of the tree. So from an infected tree with oak wilt to an uninfected tree. So it can spread underground to many oak trees. 

Tell me a bit more about where oak wilt has been discovered.

It was discovered on Belle Isle, which is in the river just between Windsor and Detroit. It's 500 metres from the Ontario border. It's a very cryptic disease. It's very hard to detect, like most forest pathogens. It's not like a bug you can see and stomp on. It might appear, and you may not know it's there for quite some time. When it is discovered, it could be widespread and very hard to eradicate.

We have no real cure for it. There's no magic bullet that will stop a lot of these invasive forest pathogens. 

How fast does oak wilt kill the tree?

It kills the trees really quickly, or it can. In the States, it's killed them as quickly as two or three weeks. But most of the time, it takes a year for the tree to die. So if a tree was to become infected during the summer, you probably wouldn't even notice that the tree had problems until the following spring when it didn't leaf out. That's when most people would sort of wonder "why isn't my tree growing?" or "why don't I see leaves on it?" 

What would losing oak trees mean for the ecosystem?

A great deal. A lot of wildlife depend on oak trees. The biodiversity that we're losing in the province already — everybody's familiar with emerald ash borer now and Dutch elm disease and butternut canker and American chestnut blight. Losing oak alone is quite significant, but when we lose all these other species at the same time, that's a big stress on the environment.

What should we do and how do protect trees if oak wilt enters Ontario?

There is no magic bullet, as I said, and that's the difficult part. Control and eradication is very expensive and often doesn't really work. So the best thing we can do is protect ourselves by — which we are doing with the Canadian Food Inspection Agency — restricting the movement of wood across from the American border into Canada.

Fungus on a tree.
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)

But my fear down in Windsor and Detroit area where it could inadvertently be brought across by firewood, or possibly, since it's so close, an insect that's blown with a strong wind. Once it takes hold, it could be here and very expensive to control.

The other aspect I think that everybody can do is be aware of disease. So when they see the symptoms, which is trees dying from the top, having oak leaves on the ground during the summer, a lot of leaves falling off early in the season, that would be very unusual for oak trees. 

So to be aware some of the signs and symptoms and and let the authorities know, which would be the Canadian Food Inspection Agency.