The latest infestation threatening Vancouver’s trees

On an overcast August morning at Columbia Park — in the shadows of the new highrises surrounding Oakridge Mall — a street-side ash tree looks to be undergoing a science experiment, with opaque tubes sprouting out all around the tree’s base. 

This is how the park board is responding to a new insect infestation threatening Vancouver’s trees. It’s one of about 40 ash trees around the park and 200 across the city being treated with an insecticide to combat a bug that was only identified in B.C. recently. 

In the summer of 2023, a citizen scientist serendipitously discovered the “highly destructive” emerald ash borer (EAB) in a Chinatown park. EAB is an exotic species of beetle that infests and kills ash trees. That “complete fluke” of a finding triggered the Canadian Food Inspection Agency (CFIA) to conduct surveys and eventually confirm that the insect was infesting ash trees in Vancouver, Sophie Dessureault, the park board’s Integrated Pest Management Coordinator, told Vancity Lookout. 

While a bug like EAB doesn’t pose a direct health risk to humans, insect infestations in trees can have a big secondary impact. City dwellers rely on urban trees and forests for shade, cleaner air, and a connection to nature, among other benefits.

In Stanley Park, a 2020 outbreak of hemlock looper moths affected at least 160,000 trees — about one-third of the park's forest. Over 11,000 of those have been cut down for fear of the compromised trees falling on people or roads, or fueling a forest fire. The final phase of logging is planned for this fall and winter, pending a court case against the removal plan. 

However, unlike the looper moth, there’s an insecticide treatment that’s effective against EAB and can be used with limited risk to the trees, people, pets, wildlife, and the surrounding environment. 

Called TreeAzin, the insecticide’s active ingredient is derived from the seed of the neem tree, and has been used in agriculture for centuries, Dessureault said. It works by killing the EAB larvae that live and grow in the tree’s trunk. The delivery system is also an important factor for the safety and scope of the operation.

“It goes right into the tree trunk… there's no spraying, no drift, [and] nothing else can get in contact with it,” Dessureault explained.

“With EAB, we're fortunate to have this treatment… and to be able to do the injection. With the looper moth, we would have to do spraying. And if you think of the size of the trees, I don't even want to try to think about what kind of operation we would have to muster to do treatments like that,” Dessureault added.

In addition to Columbia Park, other areas that have been treated this month include Coopers’ Park in Yaletown, Strathcona and nearby MacLean Park, Andy Livingstone (where EAB was first discovered in B.C.), CRAB Park, Slocan Park in Renfrew-Collingwood, and Sunrise Park in Hastings-Sunrise. 

Emerald ash borer was first found in Canada in 2002, but only in eastern provinces. “Their forest was predominantly ash trees, so they got decimated,” according to Dessureault, who said that, without treatment, EAB infestations kill 99 per cent of the ash trees they inhabit. 

EAB “​​has already killed millions of ash trees in regulated areas in Canada and the United States and poses a major economic and environmental threat to urban and forested areas of North America,” according to the CFIA. 

Luckily, unlike in eastern Canada, Vancouver has a relatively small number of ash trees. There are about 8,100 of them on public land, which accounts for roughly five per cent of the city’s trees, Dessureault said. 

Kensington-Cedar Cottage has the most ash trees of any neighbourhood in the city, with about 1,200 of them, or roughly 15 per cent of all the ash trees on city land. Nearly all of Vancouver’s ash trees are ornamental — not native to the local ecosystem.

Since emerald ash borer beetles can fly from canopy to canopy, once the park board identifies one infested tree, Dessureault explained they can safely assume the bug might also be in nearby trees. Ash trees with a diameter of 30cm, with more than 70% of its canopy still intact, and within 250 metres of an infested tree, are eligible for the insecticide treatment. 

“It's not easy to figure out which particular tree [EAB] is in… [because they’re] very high up in the canopy and inside the tree,” Dessureault said.

While the injections treat infested ash trees, using the insecticide on the surrounding trees works like a vaccine, protecting them from the worst of the infestation for up to two years.

The park board will then monitor those treated trees for signs of declining health, like yellowing leaves, canopy loss, cracking bark, or damage from woodpeckers. Dessureault said there are some cases where, if left untreated, a dead ash tree would need to be removed due to risk to the public, but that would only be a long-term outcome.

Infested ash trees in Vancouver are able to tolerate EAB better than trees out east, Dessureault noted, with the caveat that it’s only been two years since she’s been tracking it here. “The trees are still declining, but it’s quite slow… we're not seeing the rapid decline [they had in Eastern Canada],” Dessureault said, which gives the park board more time to respond with these treatments. 

This month marks the first time the park board has ever treated for EAB, given that the bug was only recently discovered in B.C. They’ve budgeted $75,000 for this year’s treatments. Dessureault is cautiously optimistic that the funding will be maintained in the future. “I know there's definitely a high interest in preserving our urban forest, so I'm not anticipating any issues. But, like everything, funding is not unlimited,” she said.

While the park board is making moves to protect the large, healthy ash trees on city land, that only represents part of the battle to protect them against this new invasive insect. Trees on private property are not part of the park board and city’s purview, so individual land owners need to get involved in those cases.

Dessureault, working with the Invasive Species Council of British Columbia and the BC Landscape and Nursery Association, is putting together some resources for homeowners to identify ash trees and what to do if they’re concerned that an ash tree on their property might be infested. 

Those resources will be posted on the city’s website, Dessureault said. If residents suspect an infestation, they can get in touch with the city through 311 or contact the CFIA. 

Another way to stop the spread of EAB in B.C. is by not transporting firewood or any material that could contain ash wood outside the city. Since its discovery, the CFIA has imposed regulated areas prohibiting the movement of ash and firewood outside city limits in Vancouver, UBC, Burnaby, New Westminster, and Surrey.