700 ash trees will fall as jumping tree lice spread through Winnipeg

Hundreds of ash trees are being removed from Winnipeg neighbourhoods as the city's forest canopy is hit by another invasive species.

The cottony ash psyllid — also known as jumping tree lice — has been added to a list of threats to Winnipeg trees, which also includes the emerald ash borer and Dutch elm disease.

"About 700 black ash trees are going to be removed," city forester Martha Barwinsky said Wednesday.

"These are black ash trees that we identified last year that were either dead or almost dead because of the cottony ash psyllid infestation."

The 700 trees are being removed primarily from Riverview and River Heights, but the insect was first found around The Forks in 2017. Evidence of the insect has since been found "pretty much throughout the city, just in varying degrees depending on the neighbourhoods," Barwinsky said.

The insects are about three millimetres long (only slightly larger than an aphid). They have yellow and black markings, clear wings with shading toward the tip, and can jump, a provincial website about invasive species says.

They infest Manchurian and black ash trees. When eggs hatch in spring, the nymphs (immature insects) suck the sap out of new leaves, causing them to curl, and produce a white cottony substance.

A second generation of nymphs that hatches in August then feeds in the curled leaves created by the first generation.

The insects weaken trees, leaving them vulnerable to disease and premature death, although trees can recover if they're not badly infested, Barwinsky said.

Less than half of trees removed are replaced

However, Winnipeg's winters haven't slowed the invasive species down yet, she said, and they seem to thrive in hot, dry summers like the one in Winnipeg last year.

"Our ash trees have no resistance or no tolerance to these pests," she said. "There's also no natural predators."

With the additional threat of the emerald ash borer, the city has decided to simply remove the trees with the worst infestations and stop planting ash trees.

"There's … going to be some significant holes in those neighbourhoods because of the ash removals," Barwinsky said.

"We try to prioritize those areas to get trees planted right away, because it's such a hit for the residents on that street, just all of a sudden to lose their canopy."

Our staff … all they've been doing is removing trees, and it really is disheartening.- Martha Barwinsky, city forester

But the city isn't keeping up everywhere.

Barwinsky expects the city to replant fewer than half the trees it cuts down this year.

Last year the city removed 11,900 trees. Of the 5,800 removed from boulevards and parks, only 2,500 were replaced. The rest were removed from private property and natural areas, and the city doesn't replant those, either.

"It's been very difficult. I know with our staff, for the past three years in particular, all they've been doing is removing trees, and it really is disheartening," Barwinsky said.

"We would much rather be planting trees, or pruning trees and maintaining them."

On the bright side for forestry staff, extra funding from the city to catch up with a backlog of Dutch elm removals means this year, they'll finish cutting those sick trees down by the end of May, Barwinsky said.

"We'll be able to give [staff] a bit of a reprieve from all the tree removals and actually do something where we're putting back into the canopy rather than always removing."

Protecting private trees

The trees they plant will be a variety of species — part of the city's problem is that it planted American elms widely in the early years, and then when Dutch elm disease became a problem, started replacing elms with ash trees.

The list of trees the city plants includes lindens, maples, oaks, willows and even some elms that are resistant to Dutch elm.

Private property owners can consult a private arborist about the health of their own trees and possible treatments for disease, or to plan replacements.

The non-profit Trees Winnipeg (formerly the Coalition to Save the Elms) has a program that encourages property owners to plant trees. The deadline for the program is May 1. More information is available at treeswinnipeg.org or by calling 204-832-7188.

Barwinsky also wants people to know that it is illegal to take ash material outside of city limits under federal regulations, or to take any type of firewood out of city limits. The forestry branch also asks people not to move firewood or wood around the city to slow the spread of pests.

No one should store elm firewood and an elm pruning ban is in effect now until July 31.