Winter temps help fight against ash tree beetle: city forester

Winnipeg’s cold winters appear to be slowing down an invasive beetle that experts once feared could wipe out the city’s ash trees within a decade.

Emerald ash borers were first detected in Winnipeg in the fall of 2017, when the city deemed the species a major threat to destroy hundreds of thousands of ash trees. At the time, there were about 101,000 ash trees on city property and 256,000 private and natural ones.

Emerald ash borers can damage the structure of the wood and put an infected tree at risk of collapsing.

Almost eight years later, the city has been surprised to find few infested ash trees required removal.

“Historically, with all other cities that have been attacked with emerald ash borer… there’s been a very rapid increase in population and a very rapid increase in (tree) losses within the first five years… We’re not seeing that here. We’ve only found it in and removed approximately 20 ash trees,” said Martha Barwinsky, the city’s forester.

Research has begun to explore why Winnipeg has been an anomaly in the spread of the invasive beetle. At this point, it appears cold winter temperatures are to credit for slowing the creatures down, said Barwinsky.

“(With) lab studies, they were finding that the beetle would be able to survive from about -30 C to -45 C temperatures… (So the cold is) not so much reducing the population, it’s actually just slowing the increase in how the population is building,” she said.

Barwinsky said it appears to generally take two years for the emerald ash borer to grow from its larval to adult stage in Winnipeg, while the beetle is capable of completing that cycle in just one year.

City crews also cull out ash trees on public property that are in poor condition and inject healthy ash trees with insecticide to combat the beetle’s spread.

“There’s potential that might also be contributing to slowing the spread,” said Barwinsky.

Unfortunately, she said the bugs are expected to adapt to the colder climate over time and climate change is expected to result in shorter cold snaps in the future.

There’s no indication the destructive pests can be eradicated.

“Once it’s here, it’s here,” said Barwinsky.

About one-third of Winnipeg ash trees are on public property. The city advises landowners with ailing ash trees to have them inspected by an arborist.

In cases where the tree appears infected by emerald ash borers, symptoms of which can include D-shaped holes in the trunk, extensive woodpecker damage, sprouting of new branches along the trunk and general “die-back,” residents are asked to report the issue to the city online at wfp.to/Wi6.

joyanne.pursaga@freepress.mb.ca

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