Work underway on treating invasive Japanese knotweed  

Herbicide glyphosate being used on weed that can choke rivers, displace natural plants

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The war on Japanese knotweed has begun with spraying of the herbicide glyphosate on public land in the Sea to Sky corridor.

An invasive species not native to the region, Japanese knotweed can have serious environmental, safety and economic impacts. The aggressively growing plant can cause so much property damage that in the U.K. would-be homebuyers cannot get a mortgage if it's present in the area.

The weed can choke rivers and streams, displace natural plants that are important to the ecology, and is incredibly hard to remove. Even a small sliver of root left behind is enough to start a new outbreak — hence the use of a chemical herbicide rather than removing the plants by hand.

Kristina Swerhun of the Sea to Sky Invasive Species Council (SSISC) said most of the work is being carried out on Crown land along the sides of the Sea to Sky Highway, where for weeks there have been yellow signs notifying drivers of the presence of Japanese Knotweed.

"It is our highest priority plant right now," Swerhun said. "It can grow three to four centimetres a day, through asphalt, cement, drainages — anywhere with cracks. It can be a huge burden to taxpayers."

The SSISC, a non-profit society dedicated to minimizing the threat of invasive species in the corridor, secured funding this summer to hire crews for a 12-week program that includes eradication. In some cases, said Swerhun, there won't be outright spraying, which would impact all vegetation in the area, Some individual knotweed plants can be injected at the root with the herbicide.

"It will not be the case of chemical control the whole time, but where it needs to get taken down it gets down," Swerhun said.

"This is one tool in our toolbox and we use it when we need to. The signs along the highway were placed there to show contractors mowing the sides not to mow in these sections, which would make it more easily spread."

The Sea to Sky corridor is part of an area that has a Pest Management Plan (PMP) that provides regulations for an integrated pest management approach to managing invasive species on crown land.

Work has been focused in the Squamish area, with a schedule of herbicide treatment and PMP details on the SSISC website,, under the tab "Field Work."

"This one plant causes so much destruction. It can actually cause safety problems because of sightline issues. Residents have called us and said they can't get out of their driveways because they can't see the road," Swerhun said.

In a release, the SSISC said that glyphosate "is a non-selective herbicide, which means it will target all plants, native and invasive," but it's non-residual and rapidly degrades, principally through micro-organisms. It is also non-persistent in soil and water.


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