Saskatoon steps up fight on tree killing pest

The Cottony ash psyllid is a tiny yellow-green pest that first arrived in Saskatoon back in 2006. This year it will claim 1,000 trees.

Highly visible tree cull underway in the city

Mature ash along 20th Street in Saskatoon's Riversdale neighbourhood are being cut down due to the Cottony ash psyllid, a pest that first arrived in the city in 2006. (CBC)

Saskatoon's urban forest is under attack by a foreign invader.

"It feeds by sucking the juices out of the plant tissue," said city entomologist Jeff Boone.

This vampire-like invader is the Cottony ash psyllid, a tiny yellow-green pest that first arrived in Saskatoon back in 2006. This year it is expected to claim 1,000 trees in the city.

The pest targets mostly black and mancana ash, of which there are about 7,000 in the city.

It will be a slow process to rebuild our urban forest.- Jeff Boone, Saskatoon city entomologist

This sort of attack on an urban forest can sometimes be hard to spot, but city hall has concentrated its counter attack on the Cottony ash psyllid in some very high profile areas, like Riversdale.

"The 20th Street example is just like a small segment of the number of trees that are going to be removed," Boone said. "We expect there will probably be more removals to come."

This photo shows psyllid eggs on the bud of an ash tree.

Infestation is city wide

Boone said there are susceptible trees in all neighbourhoods. This year, though, the destruction will be highly visible. 

"These are areas where it's tough to get trees established, it's tougher growing conditions and the loss is both higher cost removal and replanting, but also it is very significant for those streetscapes, because downtown streets it really changes the feel when you remove the tree canopy."

Only trees found to have lost more than half their foliage will be removed. Trees with less damage will be left, in hopes they might recover. Susceptible tress will be injected with an insecticide to try to keep the Cottony ash psyllid from taking root.

Boone acknowledged the battle against the bugs can be hard to watch.

"Typically we don't have removals on the scale of 1,000 a year, so the replants will be coming in but it will be a slow process to rebuild our urban forest," he said.

with files from Saskatoon Morning