Public urged to report Japanese knotweed

Posted on: July 21, 2017


A new invasive plant species – Japanese knotweed – has been spotted in Lanark County, and the public is urged to watch for and report it so steps can be taken to minimize its impact.

“Japanese knotweed has become a big problem in other parts of Canada and the world,” explains Lanark County CAO Kurt Greaves. “The damage done by this plant to foundations, septic systems and asphalt has been well documented. We all need to be proactive and work to eliminate this plant before it causes infrastructure damage and lowers property values.”

Michelle Vala, the county’s vegetation management intern, explains Japanese knotweed is highly invasive and originated from eastern Asia. “It is regarded as one of the world’s top invasive species. It forms dense thickets of bamboo-like vegetation and has extensive rhizome or root systems. It is a problem when it comes to infrastructure because it has been found to grow through eight-centimetre thick concrete or asphalt.”

She adds the plant has been identified throughout the county and is commonly found in gardens as an ornamental plant. “People should avoid purchasing it from nurseries. In Ontario, it is illegal to import, deposit, release, breed/grow, buy, sell, lease or trade Japanese knotweed.”

Japanese knotweed has heart-shaped leaves and sprouts, often mistaken for asparagus, that have a reddish tinge. The stem is hollow and turns green as it develops. In summer, they produce cream-coloured flowers. It spreads with rhizomes, so shoots will pop up all over a garden. Because it penetrates deep into the ground, it can damage foundations, drainage systems and walls.

“In addition to the infrastructure damage it can cause, it also has negative effects on habitat,” Vala added. “It degrades areas next to streams and rivers and can interfere with recreational activities by impeding access. It also out-competes native plants and negatively impacts wetland quality.”

Lanark County has adopted a new Vegetation Management Plan that uses various methods to control invasive species. The goal is to maintain safe roadsides using a long-term, multi-faceted and holistic approach. Part of the plan includes identifying and reporting invasive plants and noxious weeds. The public is encouraged to use the online mapping system at to report Japanese knotweed – or any other invasive plant or noxious weed – if they see it.

Japanese knotweed is one of six target weeds for the county, along with wild parsnip, poison ivy, giant hogweed, dog-strangling vine and phragmites.

Eradication requires a combination of cutting down the stems and chemical treatments (herbicides). “For those opposed to using herbicides, small or young infestations may be removed by digging up the rhizomes,” Vala says. “For large infestations, however, excavation would be required since the entire plant can regrow from very small rhizome fragments.”

Read the Ontario Invasive Plant Council’s information about eradication and best practices. 

4 thoughts on “Public urged to report Japanese knotweed

  1. Jean Guy Belanger

    My neighbor has what seems to be this knotwood plant.When I moved to my residence for 25 years ago, I had this plant growing through the pavement & around the foundation. Removing it from the foundation was easy due work being done in that area. In the back was a different story, my friend & I dug over 5 ft deep to remove 2 tree like plants. Today due to my neighbors negligence he’s got these useless & damaging trees growing everywhere. I had to force him to cut one because of it was damaging my roof. Now they’re spreaded all over his property & growing rapidly causing more problems to other neighbors due to his disregard & ignorance to deal with it. Is there anything I can do to have him remove this damaging plant?

  2. Brenda Orton

    W had a terrible time with this far reaching and fast spreading plant at our last residence. Not sure if it is still growing there or not but impossible to get ALL the roots! Lombardy, Ontario.

  3. Sharon Crockett

    We have had Japanese Knotweed growing on our property . We live on the bank of a bay and it is in the ravine near a water source that leads to the bay accross the road . We called years ago , they came and looked at it and that was it. We are seniors and can not remove it now.. Too little to late around here. Port Rowan, ON. Canada

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