City braces for new tree scourge

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City entomologist Taz Stuart holds an emerald ash borer in his finger, which could destroy a large population of city's ash trees. (RUTH.BONNEVILLE@FREEPRESS.MB.CA )

More than three decades after Dutch elm disease hit the province, forestry experts are working on an action plan to protect Manitoba's trees from another insect invader -- one with an appetite for ash.

The emerald ash borer has destroyed millions of ash trees since landing in North America, hitching a ride in wood shipments and devastating forests in the United States and Canada.

Despite efforts to keep the bug at bay, it's likely to hit Manitoba in the next five to 10 years, although officials say it could arrive at any time.

"It could be here as quick as a load of firewood coming through the border right now, for all we know," said Glenn Peterson, the province's manager of forest health and renewal.

The invasive freeloader has taken hold in parts of Ontario and Quebec, and caused a stir in St. Paul, Minn., after being found there for the first time earlier this summer. Manitoba is especially vulnerable, blessed with natural stands of green ash and plenty of ash trees within Winnipeg, planted to replace elms lost to Dutch elm disease.

"We've contributed to the problem, essentially, by planting a monoculture in response to a previous problem," said Peterson.

City forester Martha Barwinsky said the ash borer could easily inhabit trees for a few years before being detected.

"It could be here already and we don't know it," she said.

Barwinsky's office is in the final stages of a plan to help Winnipeg deal with the emerald ash borer, and it starts with a tree inventory. The city is believed to have around 200,000 ash trees, some a century old, and around half on city property. But since nobody has ever counted them, the estimate is just an educated guess.

To come up with a better figure, two teams of students spent the summer scouring boulevards and parks, meticulously jotting down notes about every tree they encountered, including size, condition, location and species.

The students tallied up 80,000 trees, and the inventory should take another two years to finish, Barwinsky said. It's not just about arriving at a total, but figuring out the cash value of the whole leafy canopy. A mature tree can be worth $12,000 to $30,000, depending on age and location, based on calculations by the Council of Tree and Landscape Appraisers.

Winnipeg's EAB strategy is awaiting council review, but involves figuring out what to do and who to call if the bug is found, costing out tree removal and deciding which ash trees are top priorities. The report recommends the city start monitoring for the borer next year, "which means we'd have to have two staff members solely dedicated to active EAB monitoring, said Barwinsky.

Symptoms of infection are fairly general, she said, meaning trees that are simply unwell can be mistaken for those sheltering the insect. And it's impossible to know for sure if the pest has infected a tree without doing "destructive sampling," peeling back the bark and looking underneath. The few times the city has tested ash trees, they've found none of the trademark tunnels, called larval galleries.

Manitoba has spent more than $50 million tackling Dutch elm disease since it arrived in the 1970s, and the cost of keeping damage to a minimum runs around $2 million annually.

Officials don't know what it will cost to fight the emerald ash borer, but some cities face a hefty price tag: St. Paul estimates it would need another $3 million annually, according to local media reports.

The province is in the midst of setting up an ash borer committee with the Canadian Food Inspection Agency, Winnipeg forestry officials and other groups, and a delegation will head to St. Paul this fall to check out their response. Provincial staff is also gathering material to get arborists and survey crews up to speed.

Jeffries Nurseries owner Wilbert Ronald said he's been preparing for the borer for five years, dropping production of ash from 40 to 20 per cent of total tree sales and researching alternatives, such as more maple, linden or hackberry trees.

Peterson said the Forest Health Protection Act could allow for a ban on fuel wood shipments into Manitoba unless it had been properly treated, following industry consultation. For now, people can voluntarily drop off firewood when they enter the province.

Keeping the emerald ash borer out of Manitoba completely might be a pipe dream, but Peterson said he thinks the province stands a chance with good monitoring and fast action.

"I think it's realistic to think that we can delay its introduction here, and hopefully by doing a proper job of surveillance and rapid initial attack, be able to control it," he said.

lindsey.wiebe@freepress.mb.ca

What is the emerald ash borer?

The metallic green beetle arrived in Michigan in 2002. It's believed to have come from Asia in packing crates, and, although it can fly, the bug is spreading through shipments of lumber, firewood or nursery stock, experts believe.

What's the damage?

The emerald ash borer can hide in a tree for years without detection. Larvae do the most damage, burrowing under a tree's bark and eventually killing it by cutting off the flow of nutrients. The borer has left an estimated 20 million dead trees in its wake in Canada and the United States.

How can I tell if my trees are infected?

Not easily. It's tough to know whether a tree is simply unhealthy or if it's infected with EAB. The borers do leave a tiny D-shaped entry hole in tree trunks, and infected trees might grow shoots from the base of their trunks, says city entomologist Taz Stuart. S-shaped larval galleries can also show up in a tree's bark. The best way to protect trees is to stop the spread, officials say, and the easiest option is to stop carrying firewood into or out of communities.

Republished from the Winnipeg Free Press print edition August 31, 2009 B1