'Jumping tree lice' threaten more than 14,000 Winnipeg ash trees

Beleaguered Winnipeg trees are under a fresh attack from a new foe this season: the cottony ash psyllid, also known as jumping tree lice.

The tiny, yellow-and-black bugs were first spotted in city trees last year, but their impact was considered low at the time, said city forester Martha Barwinsky.

That changed this year thanks to a dry season, she said, although city tree experts are still determining the extent of the infestation.

"This spring, of course, a lot of the black ash trees were very late to leaf out, much like last year. But as they started to leaf out, the impact was even greater," she said. "We're finding, actually, much more advanced stages of the cottony ash psyllid this year."

The three-millimetre-long bugs have been found throughout North America for roughly a century, Barwsinky said, but they're a relatively new addition to a growing roster of dangers facing Winnipeg's tree canopy.

Barwinsky told CBC News last year the city had reached a "critical point" in managing the spread of Dutch elm disease, and tree experts also found the first specimens of the destructive emerald ash borers in city trees.

With cottony ash psyllids — also called jumping tree lice for the way the adults jump — Barwinsky said roughly 14,400 public trees are at risk. A little over 10,000 of those are black ash trees, the bug's preferred host, and the rest are mancana ash or black-mancana hybrids.

Pest-fighting results 'not terribly effective'

In their nymph stage, the psyllids live inside or underneath trees' leaves, curling the leaves up and filling them with a cottony substance, Barwinsky said. They suck the sap out of the leaves and give them a distorted appearance and "cauliflower-type texture."

"With repeated infestations or severe infestations, particularly in stressed trees, it definitely can kill the trees," Barwinsky said. "And that's what we're actually finding, is that there are black ash trees that have died as a result of this pest."

Barwinsky said there's little the city can do to stave off the bugs.

Cottony ash psyllids have already been found in Canadian cities including Edmonton and Saskatoon, she said, and efforts to manage the bugs there "haven't been terribly effective."

"Other cities have been trying some tree injections to protect the trees or kill the pest, and their results have been very sporadic," she said.

City foresters are in the process of determining how much it will cost to remove affected trees this year and next year, she added.

Despite the onslaught of pests, Barwinsky said she's hopeful for the future of the city's trees.

"We have an incredible, valuable asset here in Winnipeg with our urban forest," she said. "And we just have to keep on top of it to keep that canopy over our city."