Maple Ridge should take knotwood invasion seriously

Invasive Species Council says the weed can bust through concrete

While Maple Ridge parks director David Boag told council last week that he’s never seen evidence of Japanese knotweed boring through concrete, it does happen, says the Invasive Species Council of Metro Vancouver.

Jennifer Grenz, projects manager with the council, said the plant can go through concrete, and does.

“There are billions of pounds put into [fighting] this plant in the U.K.,” said Grenz who e-mailed several articles and photos showing the potential impact of the plant.

Included was one story from the BBC from Oct. 27, 2011 (, showing knotweed growing inside a house that had sustained $250,000 damage and that three metres of soil had to be removed from beneath the building.

The photos showed shoots of the plant punching through asphalt and climbing out of concrete block retaining wall.

Boag told council last week that if the plants are too close to a house, they could ruin the foundations.

But he said knotweed is one of many invasive plants the district has to deal with, noting that giant hogweed, which can cause serious burns or blindness, is another.

Boag also told council  that a committee is developing a noxious weeds strategy and that he’s been in touch with other cities and the Invasive Plant Council to discuss solutions and costs.

Grenz, though, wanted to ensure the public understood the potential impact in Maple Ridge and not to take it lightly and planned on contacting the district again.

The only way to kill Japanese knotweed is by direct injection of the herbicide glyphosate into the stems, a treatment which may require more than one application before the plant is killed.

Cutting the plant only spreads it more while it’s impossible to dig out because the roots run so deep.

Grenz said the invasive species council reaffirms the potential of knotweed to break through concrete and pointed out the council takes direction from the provincial government.

“In regions where it exists, the provincial government has prioritized the treatment of this particular plant over most others because of its threats to infrastructure, public safety and the environment and the resulting economic costs,” Grenz added.

“We stand by what we say about the potential of knotweed to cause significant damage to infrastructure including its ability to break through concrete.”

She said that given the impact its had in the United Kingdom, “Our organization hopes that by finally getting the message across about the seriousness of this plant, we can prevent a similar story from happening in the Metro Vancouver area.”