It's already devastated ash trees in southern Ontario and parts of the United States since it was first seen in North America in 2002.

And now the City of Winnipeg is preparing for the arrival of the emerald ash borer, an invasive beetle that originated in Asia, which eats and kills all species of ash trees.

"It has the potential to kill all of the ash trees in the city of Winnipeg," said Martha Barwinsky, the city's forester.

The ash borer hasn't been found in Manitoba yet, but city crews have been out taking inventory of the city's ash trees on private property since last May.

The city estimates that there are about a quarter of a million ash trees in Winnipeg most of them being green, black, or Mancana varieties. City forester Martha Barwinsky stands next to a black ash, the city's second-most common type of ash tree. She says more than 30 per cent of Winnipeg's tree population on boulevards and in parks is ash. (Holly Caruk/CBC)

"We know that over 30 per cent of our tree population on boulevards and in parks is ash, so when you think of 30 per cent of the canopy, 30 per cent of the trees dying and being removed … that's is a significant part of our urban forest," said Barwinsky.

A 2013 inventory estimated that there are over 200,000 hectares of natural ash stands throughout the province of Manitoba.

The insect has gradually been making its way west. Barwinsky says the beetle has been found as close as Thunder Bay, Ont., in the east, and Duluth, Minn., to the south. That puts the beetle within a few hundred kilometres of Winnipeg.

She says it's just a matter of time before it shows up here.

"It's just inevitable. It may very well be here already and we just haven't found it," she said. It's already devastated ash trees in southern Ontario and parts of the United States since it was first seen in North America in 2002. And now the City of Winnipeg is preparing for the arrival of the emerald ash borer, an invasive beetle that originated in Asia, which eats and kills all species of ash trees. 1:04

"It's very difficult to detect. A tree may be infected with emerald ash borer anywhere from three to five years before you can actually see symptoms in the tree, or find signs of the beetle. So it is very well hidden," said Barwinsky.

The adult beetle, named for its emerald green colour, feeds on the foliage of the tree but it's the larvae that do most of the damage. The ash borer larvae feed on the tissue of the tree beneath the bark, preventing water and nutrients from circulating throughout the tree and eventually killing it.

The beetle also has few effective predators, which has allowed it to spread through much of southern Ontario and Quebec as well as parts of the U.S.

Some neighbourhoods could be hit hard

The city says there are 101,000 ash trees on public property throughout Winnipeg. The private property survey that began last year will provide a better picture of how many ash trees are in people's yards, though the city estimates there could be 150,000 ash trees on privately owned land.

Areas like River Park South, Dakota Crossing, Tyndall Park, Lindenwoods and Richmond West all have high populations of ash on city land. City of Winnipeg employees are taking an inventory of the city's ash tree population on private properties. (Holly Caruk/CBC)

​If a tree is infested with ash borer beetles, there are a few tell-tale signs, says Barwinsky.

"Looking for a D-shaped exit hole — so these are actual holes in the bark of the tree. The beetles emerge around May, June and because they are a flat-headed boring insect … their cross section is in a 'D' shape, so when they emerge from the tree they leave a D-shaped hole," she said.

Barwinsky says another sign is split bark on the trunk or branches, and that you may be able to see the serpentine tunnels where the larvae have gone through.

Homeowners who think their tree may be infested with the beetles are asked to call 311.

What can be done?

Barwinsky says there are essentially only two options once a tree becomes infested — to remove it, or treat it with an injectable insecticide.

"Injection is costly but if it is a high-valued tree and it's worth treating it, then homeowners have chosen to do that and cities have chosen to do that as well," she said.

The city still does not know if or how a city-wide injection plan would work, but the costs would likely fall to the homeowner. Once the treatment begins it needs to be done annually at first, and then every two years.

The city expects the battle to last for years once the insect is discovered here.

"It takes about 10 years for the beetle, once it is found, to actually infect and kill almost all of the ash trees," said Barwinsky. Serpentine tunnels where emerald ash borer larvae have gone through are a sign a tree is infected with the beetle. (Kate Porter/CBC)

She says while the arrival of the beetle is inevitable, there are things people can do in the meantime.

"Don't transport firewood. If you've removed a tree or you have firewood, burn it where you bought it, burn it where you cut the tree down," she said.

Once the beetle is here, though, the problem can only be managed.

"We will not be able to eradicate it," she said.

"What you're doing is managing the mortality of your ash trees over that period of time, so you're spreading out the costs and spreading out the removals and replacements."

City encourages replanting other species

People are encouraged to plant new trees on their properties to help offset the damage. The city has also discontinued the planting of ash trees on public property, and up until last year were only planting the Mancana ash, which is thought to be more resistant to the borer, but not immune.

"Once we learned about emerald ash borer, we started working on improving the diversity of our urban forest," said Barwinsky.

"We are planting with elms, we are planting with maple, with linden, with hackberry, and burr oak if we're looking at the shade trees. And then a wide variety of smaller and medium-sized ornamental trees," she said.

After losing thousands of trees to Dutch elm disease in the past few decades, the city has changed the way trees are planted in neighbourhoods. This map shows where ash trees are located throughout Winnipeg. Each green dot represents an ash tree (green, black, or Mancana) on city-owned property. There are an estimated 150,000 ash trees on private property, which are not displayed. (Jacques Marcoux/CBC)

"After Dutch elm disease was discovered here in 1975, there were a lot of neighbourhoods that were planted solely with ash," Barwinsky said.

"A monoculture of trees is not healthy for the urban forest … if we do have a species-specific pest attack, then we have a large loss of canopy, which is what we're seeing with Dutch elm disease."

Now the city ensures a variety of trees get planted in new neighbourhoods to help avoid a similar situation in the future.

The value of trees

The city says the ash borer could cost millions of dollars to manage, but no firm estimate is available yet. Other similarly sized cities have spent upwards of $6 million annually to fight the emerald ash borer.

The Canadian Forest Service estimates that costs for treatment, removal and replacement of trees affected by the emerald ash borer in all Canadian municipalities could reach $2 billion over a 30-year period.

Winnipeg's boulevard and park ash tree population has an estimated value of $437 million.

The city says it would also experience significant losses of environmental, economic, public health and social benefits, as the whole urban forest could be impacted.

"Reduced heating costs, reduced cooling costs, even just the aesthetic value and the feeling of community, the shade that we get from the trees, and even just the habitat in our neighbourhoods," are all things that could be lost, said Barwinsky. Ash trees make up about a third of all tress on city properties. They are usually one of the last trees to grow their leaves in the spring, and one of the first to lose it's leaves in the fall. (Holly Caruk/CBC)

The city has partnered with Trees Winnipeg, formerly the Coalition To Save the Elms, to help residents plant new trees on private property. The Winnipeg Releaf Program provides an assortment of tree packages for $55. The cost includes a workshop on how to plant and care for your new tree as well as some followup care.

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