Concrete-busting weed can threaten projects

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by Jean Sorensen last update:Aug 30, 2012

Japanese knotweed, capable of busting through highways, meridians, concrete foundations and even metal, has been added to the B.C. Weed Control Act, which means landowners must control the plant.
Concrete-busting weed can threaten projects

Japanese knotweed, capable of busting through highways, meridians, concrete foundations and even metal, has been added to the B.C. Weed Control Act, which means landowners must control the plant.

This has ramifications for the construction industry, said Jennifer Grenz, program manager for the Invasive Species Council of Metro Vancouver.

The plant can wreak havoc on a contractor’s guarantee and add substantial costs to a project.

Chemical eradication is required and several treatments may be necessary over a year long period.

“We are trying to get the word out to the construction industry,” said Grenz, who pointed to the London Summer Olympic’s velodrome and aquatic centre site, which was plagued by the destructive species.

In March 2007, the Daily Mail online reported on the issue.

“Japanese knotweed could add £70 million ($109 million) to the cost of staging the 2012 Olympics. Specialists can charge up to £40,000 ($62,570) to clear only six square yards of ground affected by the weed, which has been called the most invasive plant in Britain.”

The plant is being blamed for part of the cost over-run for the site development, which included demolishing structures, building tunnels, clearing up contamination and constructing the aquatic centre and the velodrome on the site.

In early August, Hatch environmental consultants announced it had been hired by the Port Mann/Highway 1 Project in Metro Vancouver to deal with weeds, such as knotweed, along the 37-kilometre corridor.

“Japanese knotweed, recently designated as a noxious weed, resists most non-chemical attempts to eradicate it and is a management challenge, said Hatch in news release.

Robin Taylor, Hatch's environmental manager for the highway expansion project appeared on a CBC news video recently stating that simply chopping down a stem results in eight more growing in its place.

In the U.K., Grenz said, insurance companies will not provide coverage for building sites known to have knotweed.

“I’ve already had a call from one insurance company here,” she said, adding that B.C. is just waking up to the ramifications of the knotweed’s spread.

Originally, she said, it was believed to have come into B.C. as a garden ornament favored for its rapid growth characteristics as a privacy screen.

While the plant’s stock resembles notched bamboo, its heart-shaped leaves are different from the splayed finger pattern of real bamboo.

Japanese knotweed is now in many regions throughout B.C., in six Canadian provinces and 39 of 50 U.S. states. It is on the World Conservation Union’s list of 100 worst invasive species.

Grenz said it has a preference for cool, moist areas and therefore can be found around riverbanks and poses a threat to bridge footings.

She said the council has had training sessions with bridge inspectors, as it was recently found growing along the base of the Ironworkers Memorial Bridge in Metro Vancouver.

She has also seen it grow in areas around gravel quarries, as the plant is shade tolerant.

This poses a threat if machinery cuts the plants and then it is transported to more sites as fill material.

A piece the size of a small finger can regenerate a plant, which has roots like an iceberg, she said. The plant’s roots can travel nine metres into the ground and 28 metres horizontally.

“It’s not been a problem for our members at this point,” said Paul Allard, executive director of the B.C. Stone, Sand & Gravel Association.

Members haven’t brought the issue to his attention, but Allard said he intends to apprise his members about the weed

Educational information should be forthcoming.

“The good news is that regional districts and municipalities are developing active programs,” Grenz said.

However, there is a need to alert private landowners as well as developers and contractors.

She said it’s especially critical for contractors who are doing pre-loads and moving material onto a construction site.

Knotweed can be transported on machinery as well as within the sand, gravel, or dirt.

Grenz said municipalities at one time simply mulched the plants as it was found growing along the roadside.

“When you shred it, you are just turning it into a million new plants,” she said.

For more information about Japanese Knotweed visit Additional information is available from the Invasive Species Council of B.C.

last update:Aug 30, 2012

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