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 www.eddmaps.org/ontario/about/ 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.”