Japanese Knotweed is an invasive species of major concern. Once established, it is very persistent due to a lack of natural predators and its ability to survive Canadian winters. It is extremely aggressive in its ability to spread, and is therefore very difficult to control. Like many invasive species, it out-competes native plants and consequently poses a big threat to our local biodiversity. In addition, the plant’s root system can create serious infrastructure problems by growing through asphalt and concrete. The International Union for Conservation of Nature has named it one of the world’s 100 worst invading species.
Here is what you can do:
1) Learn to identify it: Semi-woody perennial plant capable of reaching 1-3 m (3.3-9.8 ft) in height. Stems are round, reddish-purple, smooth and have a bamboo-like appearance. Leaves are ovate with a flat base, reaching 8-15 cm (3-6 in) long and 5-13 cm (2-5 in) wide with pointed tips. Flowers are greenish-white. Fruit is small and white with wings. Seeds are brown and shiny.
2) Do not purchase it, seed it, plant it, grow it, propagate it or transport it.
3) Register your sightings of it here with the Ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs of government and then map them here on the local Lac Manitou invasive species mapping site.
4) Remove Japanese knotweed on your property by following these guidelines:
repeatedly cut down plants and new shoots, ideally using secateurs for controlled work.
place all parts of plant (root, leaves, seeds, etc.) into garbage bags, double-bagged and watertight, because regeneration can occur even from small plant fragments. Cut parts into small pieces first to ensure they don’t puncture the bags.
leave bags out in the sun for a few weeks to ensure dehydration of the plant parts.
place the bags in the trash.
do not put any plants or fragments into the compost.
do not try to pull the plant out of the ground, as it will break up in the soil and multiply.
these steps may need to be repeated for a number of years to completely kill the plant and its root network.
after removing the visible knotweed, the area where it resided can be covered with a dark tarp, to prevent sun exposure and therefore kill the root system. This tarp will need to remain in place for a few years.
5) Do not attempt to kill knotweed with glyphosate (“Roundup”) or other herbicides. It is unlikely to be successful and carries great ecological risks.
6) Clean any equipment that has come into contact with Japanese knotweed or the earth that it is in. Do not use this earth for any purpose.
For more information on this invader, please see the resource documents below created by Francesca Frati, member of the Environment Committee, or email the AALM at info@AALM.ca.
Bibliography:
City of Westmount. (2024). Invasive and noxious plants. Retrieved May 28, 2024 from https://westmount.org/en/environment/invasive-plants/
Espace pour la vie Montréal. (s.d.). Renouée du Japon : véritable peste végétale. Retrieved May 28, 2024 from https://espacepourlavie.ca/renouee-du-japon-veritable-peste-vegetale
Gerrard, N. (2021). Dehydration kills Japanese knotweed with ‘100% success rate’. Retrieved May 28, 2024, from https://constructionmanagement.co.uk/dehydration-kills-japanese-knotweed-with-100-success-rate/
Gouvernement du Québec, M. d. l. e., de la Lutte contre les changements climatiques, de la faune et des Parcs. (2024). La renouée du Japon (Reynoutria japonica). Retrieved from https://www.environnement.gouv.qc.ca/biodiversite/especes-exotiques-envahissantes/renouee-japon/index.htm
Holmes, K. (2020). These Are the Safest Ways to Get Rid of Japanese Knotweed in the Garden: Avoid toxic sprays and use our expert-approved tips instead. Martha Stewart. Retrieved May 28, 2024, from https://www.marthastewart.com/2222793/ways-eradicate-remove-japanese-knotweed-garden
OFAH/OMNRF Invading Species Awareness Program. (2021). Japanese Knotweed. Retrieved May 28, 2024 from https://www.invadingspecies.com/invaders/plants/japanese-knotweed-2/
Payne, T. (2024). How does Japanese knotweed spread? Retrieved May 28, 2024 from https://tpknotweed.com/guidance/how-does-japanese-knotweed-spread/