Thunder Bay

Green dots on trees in Thunder Bay part of battle against Emerald Ash Borer

If you have been seeing green dots on trees in your neighbourhood in Thunder Bay, have no fear. Those  trees are not being marked for removal or even pruning. Those green dots actually mean those trees are being treated against the invasive emerald ash borer.

About 800 trees are being treated with a bio-pesticide

These green dots mark ash trees in Thunder Bay being treated to fight the emerald ash borer. (Gord Ellis/CBC)

The appearance of green dots on trees in some neighbourhoods in Thunder Bay is a sign they are being guarded against the invasive emerald ash borer rather being marked for removal or even pruning according to the Emerald Ash Borer Services Coordinator for the city.

Robert Scott said the green dots are a way for the city and its contractors to identify which trees have been treated with a bio-pesticide that protects them against the pest.

Scott said not every ash tree is able to be treated and there are some criteria that need to be met.

"Essentially, the tree has to have good structure," he said. "So no deformities or wounds or existing pathogens. We also look for size as it has to withstand multiple years of drilling into the tree and heal over the wounds."

An emerald ash borer beetle adult next to a larva on an ash tree. (Government of Ontario)

Scott said they also look for any conflicts with utilities or other trees.

On its website, the City of Thunder Bay's Forestry & Horticulture Section said it manages well over 30,000 trees within the city limits. It said these trees are important assets and "provide tangible benefits to citizens and other infrastructure."

Scott said in 2017, the city had 6,300 ash trees, but only around 17-hundred of those were eligible for for treatment.

He said that has now changed with an update to the emerald ash borer management strategy that was recently approved by council.

"We've now moved to 25 percent of eligible trees and at this time there's around 4,800 ash trees remaining total," he said. "But as far as the number that will be continuing to inject it sits around 800 trees."

The truck of an ash tree on the north side of Thunder bay, Ont., being treated in the fight against the emerald ash borer. (Gord Ellis/CBC )

Scott also said some of the city's ash trees are not thriving this summer and he says a few areas seem worse than others.

"Ash this year have been particularly rough, especially in the Parkdale and Woodcrest neighborhoods," he said.

"Some of them didn't have leaves until about a week ago. So those trees are not necessarily dead, but they certainly are stressed. And we're working on determining the precise cause of that that stress."

Scott said they have set up traps for the ash borer around town to monitor the population. He said if you see a green triangular prism in an ash tree it's an emerald ash borer pheromone trap.

"The trap has something that smells like emerald ash borer and smells like fresh ash leaves." he said. "Those are checked about every two weeks during the summer for emerged adults that get stuck on that trap."

Scott said that helps the team identify emerald ash borer hotspots. In the city's most recent (2011) Urban Forest Management Plan (UFMP), from 2011, it says the goal is to create a diverse urban forest in and along streets and in our parks.

It says an urban forest of various species and ages of trees can better defend against natural and human-made threats, but many trees struggle in the northern urban environment.

On Feb. 4, 2020, The City of Thunder Bay was proudly recognized as a Tree City of the World, along with eight other Canadian cities and many more around the globe.