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Concrete-busting knotweed menaces Metro landscape

It is truly a demon weed.

Japanese knotweed, now running rampant across Metro Vancouver, can drill through asphalt, break house foundations and spring back from virtually any non-chemical attempt to eradicate it.

And it now has transportation ministry officials scrambling after it was discovered splitting concrete in the footings of the Ironworkers Memorial Bridge and infesting a Burnaby section of the $3.3-billion Port Mann/Highway 1 expansion project.

"It's a monster plant," said Jennifer Grenz, program manager at the Invasive Species Council of Metro Vancouver. "And it's a huge issue in terms of infrastructure and safety."

She said some Highway 1 construction in Burnaby from Boundary Road to Canada Way may be delayed while plants are sprayed and given time to die, adding they would otherwise grow right back up through the pavement.

The council, which manages invasive plants on local highways, is now moving to assess all provincial highway bridge and overpass footings in the region, Grenz said, and she urges local cities to do the same with their roads and bridges.

A transportation ministry spokesperson said the weed won't delay the completion of the Highway 1 project and said the infestation at the north end of the Ironworkers bridge is not serious but is being treated.

"This plant is capable of growing through three metres of concrete," Grenz said, adding she fears it could also rupture fuel pipelines where she's seen it growing.

"It can very easily grow through a pipeline, making it a very serious public safety concern."

Plenty of land slated for housing is infested, she said, adding home buyers may later find their dream home has a nightmare of knotweed growing under it because developers failed to correctly remove it.

Stem-injected herbicides are the only practical way to kill knotweed, according to Grenz, who is also a farmer in Richmond.

But she said bylaws banning cosmetic pesticide use in many cities have sown confusion over when chemicals can or should be used to kill weeds. Herbicides can be used to control knotweed and certain other species listed under the B.C. Weed Control Act, which trumps local bylaws.

Metro Vancouver lacks a coordinated regional strategy to battle introduced species, unlike the Fraser Valley and most other regions of B.C.

"Everyone is working in isolation and trying different things," Grenz said.

One park or property may be treated with herbicide, but an adjoining one isn't, defeating the investment of the responsible owner.

Grenz appeared before Metro Vancouver's environment and parks committee Wednesday, asking the regional district for a $40,000 one-time grant to help develop a regional strategy for invasive pests.

The issue was referred to Metro staff for a recommendation on whether the region should develop its own strategy or partner with the council.

Vancouver Coun. Heather Deal, the committee chair, said invasive species pose a "huge problem" that threaten native species and local ecosystems.

Japanese knotweed, which is bamboo-like with heart-shaped leaves and small white flowers, originally arrived here via garden centres that sold it as an ornamental plant that would grow easily and survive neglect.

Property owners with knotweed are urged not to try to remove it manually.

Grenz said it's almost impossible to dig deep enough to get all the roots, the plant doesn't compost well and it readily spreads – just a 200 gram stem chunk can spawn a new plant.

For more on the invasive species council or combatting knotweed see www.iscmv.ca.

 

Japanese knotweed found under the footings of the Ironworkers Memorial Bridge on the North Shore. It was immediately treated with herbicide.  Jennifer Grenz photo

Urban region highly vulnerable to invasive species

Knotweed isn't the only invasive pest raising alarms.

Giant hogweed is another problem plant that brings special control challenges because its sap causes serious burns.

The arrival of aggressive European fire ants, garden-destroying chafer beetles and the recent capture of a snakehead fish in a Burnaby pond have all increased awareness of other invading animals.

"Our region is scary-susceptible," said Jennifer Grenz of the Invasive Species Council of Metro Vancouver.

The Metro Vancouver region is uniquely vulnerable, she argues, because it's a hub for tourists and part-time residents from around the world who bring foreign species here.

Grenz said some releases of species, likely including the Burnaby snakehead, are the result of religious rites where animals or plants are deliberately released, adding more public education is needed.

Illegal dumping is also a huge cause behind the spread of invasive plants, which one yard owner chops and dumps in a ravine, park or ditch.

Grenz said some stakeholders have suggested challenges like knotweed are so onerous Metro Vancouver should instead be deemed a "sacrifice area" where authorities would give up on weed management.

That's an untenable idea, she said.

"We have such small amount of green spaces we need to protect them as much as we can."

But the invaders Grenz worries most about are the ones that have not yet arrived here.

"Any insect really scares me in terms of invasiveness. At least plants don't move that fast."

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