The knotted signs of an infestation were discovered last fall, but this week Winnipeg forestry crews found their first live emerald ash borer beetle larva tucked beneath the bark of a St. Boniface tree.

Crews confirmed a fourth infected tree on Wednesday and uncovered the first documented borer larva under its bark, said borer expert Krista Ryall.

Ryall works for Natural Resources Canada's forestry branch and is in town training city crews this week on how to spot infected ash trees through a bark-shaving method she devised.

Emerald Ash Borer Beetle Surveys in Winnipeg

Kerienne La France, executive director of Trees Winnipeg, shaves bark from a green ash branch at the City of Winnipeg's public works building on Waverley Street Wednesday. (Krista Ryall/Natural Resources Canada)

The first tree in Winnipeg confirmed to be housing the invasive beetle species from China was located on Cote Street, in the Archwood neighbourhood, in November. Crews have since found three more in the area. 

In Ontario, Ryall has watched the beetle chew through "99 per cent or more" of municipal ash populations within a decade of its arrival, spreading out a few kilometres every year from the first site of infection.

"It's a very devastating insect," she said. "You may have one per cent [of the trees] lingering for a while and then the beetle gets them, too."

Emerald Ash borer beetle infected tree Winnipeg

Borers can live beneath the bark of ash trees for more than two years before obvious signs of infection start to show. (Holly Caruk/CBC)

It was first spotted in North America in Detroit and Windsor, Ont., in 2002. It's since popped up in Montreal, Toronto and Hamilton, where it has cost municipalities millions of dollars to fight.

It's possible Winnipeg could lose all of its roughly 350,000 ash trees — 202,000 of which line city boulevards and streetsides — within that decade timeframe, too. Researchers with Natural Resources Canada estimate it could cost about $200 million for the city just to cut down and replace those 202,000 trees.

It's still early days, and Ryall said there's a chance Winnipeg's cold winters could slow the developmental stage of the beetles and thereby delay the spread.

The city also has more tools at its disposal for stemming the spread thanks to the trials and tribulations of eastern Canadian communities that were caught even more unprepared.

City gears up to fight emerald ash borer1:54

Female borers can fly 10 to 20 kilometres, Ryall said. After landing and depositing eggs on an ash tree, the larvae eventually carve out "serpentine" galleries as they develop and eat their way through the tree, Ryall said.

That's the explanation for the short-distance spread. It's humans hauling firewood or other lumber infected with borers that are likely to blame for the bug making its debut in Winnipeg.

"I would suspect that maybe what we're seeing here, somebody brought some camp firewood from an infected area, brought it here," she said.

Apart from chopping down and destroying infected trees, one management option on the table is injecting so-called "high value" trees with a vaccine-like insecticide.

City of Winnipeg forester Martha Barwinsky said the injection would help preserve some trees and slow the spread.

Emerald ash borer larva

A tiny emerald ash borer larva, found in Winnipeg in January 2018, is seen at the bottom of this vial. (Submitted by Janet Rosin)

That method has the advantage of protecting trees deemed special, although such trees need to be injected every couple of years to maintain immunity. Those costs add up — each injection runs about $165 for an average-sized tree.

Homeowners with ash trees should keep an eye out for increased woodpecker activity (they eat borer larvae) and external signs of damage to bark, Barwinsky said.

"It's tough to detect," she said, encouraging anyone who suspects they know of an infected tree to report it to 311.


The 2,000 dots on the map below are a random sample of Winnipeg's green ash trees, the second-most common tree in the city. The data reveals although the tree was widely planted across the city, there are high concentrations in newer neighbourhoods, which experts say are likely to become the problem areas with the appearance of the emerald ash borer in Winnipeg.

View the map on mobile here.