Winnipeg doses ash trees for 2nd year as destructive invasive beetle continues to spread

There's no real hope for Winnipeg's ash trees long term, but the city is doing what it can to slow the spread of the invasive emerald ash borer and the inevitable collapse of the ash canopy.

The city of Winnipeg begins its seasonal emerald ash borer management program Monday. For the second year, city crews will inject a number of healthy ash trees with insecticides meant to provide some protection against infestation.

The Asian beetle was first detected in Winnipeg in 2017, and scientists say once it gets into an urban ash canopy it can decimate the population within a decade.

"Emerald ash borer is a very destructive, invasive forest pest," said Kerienne La France, supervisor of urban forestry technical services with the city. "All of our ash trees are at risk."

At 350,000 trees, green ash is the second most common species in Winnipeg and makes up 30 per cent of the entire urban forest canopy, said La France. About 100,000 of those are found on municipal boulevards and in parks.

The city ash borer program includes monitoring, ash tree removals and injecting some on municipal land with TreeAzin or IMA-jet, solutions meant to kill ash-borer larvae that might be burrowed beneath the bark. The treatments are effective for two years, said La France.

The injection program will begin in the following insect management areas on June 17:

• Windsor Park.
• Worthington
• Kingston Crescent, Minnetonka, Pulberry.
• Southland Park.
• Island Lakes, Royalwood. 
• Vista.
• Beaumont, Crescent Park, Maybank, Wildwood.
• Central River Heights. 
• Crescentwood, North River Heights, Wellington Crescent.
• Grant Park, Rockwood.
• Minto, St. Matthews.
• Wolseley.
• Daniel McIntyre, West Alexander.
• Dufferin, Logan C.P.R., Lord Selkirk Park

About $225,000 has been allocated to fighting the borer this year, said La France.

1,000 trees to inject

Last year crews with the city's forestry branch injected more than 1,000 ash trees, and the city hopes to do as many again this year, said La France.

Damage from the borer and other pests have already led the city to chop down over 12,000 ash trees this year.

Some green and black ash were removed in response to borer concerns while others were removed due to the cottony ash psyllid, another invasive species commonly known as jumping tree lice.

Despite having such a dense population of ash trees, one saving grace for Winnipeg could be its cold winter climate. Scientists suspect really cold temperatures can slow the reproduction and life cycle of borers to two years instead of one, and that could mean Winnipeg retains its ashes slightly longer than other eastern Canadian and American cities hit by the pest.

Watch for hitch-hikers, woodpeckers

La France stressed the importance of Manitobans not transporting firewood from where it is cut down, as the invasive species can "hitch hike" in the wood and that can further the spread.

Winnipeggers should also keep an eye out for "excessive" woodpecker damage in trees, as the bird is one of the only known local predators of borers and the extra activity could be a sign of borers hiding below the bark, said La France.

Anyone with ash trees can consult a local arborist to decide how best to maintain the health of their tree or whether it's time to chop it down.

The city began planting ash after Dutch elm disease struck Winnipeg's monoculture of American elms in 1975. Ash trees then became the second monoculture in Winnipeg; it was one of the most prominent species planted in neighbourhoods developed in the era shortly after that, said La France.

Monocultures are vulnerable to invasive species, which is why La France encourages people to plant more trees of a variety of species on private property to help preserve the city's forest canopy and tree diversity.