Take a 20-minute drive just about anywhere in southeastern New Brunswick, and it is almost guaranteed that you will come across this familiar bamboo-like plant. Regarded as one of the world’s top one hundred invasive species by the Global Invasive Species Database, Japanese knotweed (fallopia japonica) is a nearly ubiquitous feature within every town along the Petitcodiac Watershed.
Japanese Knotweed is a perennial herbaceous species native to Eastern Asia. It has a hollow purple-green stem up to 2.5 cm in diameter with brown-colored nodes where new leaves or stems emerge (Anderson, 2012). It grows rapidly at a rate of up to 8 cm a day reaching total heights of 1-3 meters tall (Anderson, 2012). Leaves are alternate with an oval shape and a triangular tip and panicle clusters of white-green flowers bloom in July or August (Anderson, 2012). It was introduced to North America in the 1900s to be used as an ornamental, for erosion control and livestock foraging. Since then, it has outgrown its intended boundaries and escaped cultivation.
Able Surveyors Limited. https://www.ablesurveyors.com/blog/all-you-need-to-know-about-japanese-knotweed/
The plant forms impenetrable bamboo-like thickets which spread rapidly and dislocate native plant and animal species. Japanese Knotweed is an incredibly persistent plant featuring extensive root and rhizome structures, a horizontal root that allows it to rapidly regenerate through the surrounding soil. Under optimal conditions, these rhizomes can spread outwards at a rate of about 50 cm/year and can extend up to 20 meters laterally from the parent plant. Japanese Knotweed is most commonly spread by human and natural disturbances when soil and plant matter are dispersed. As such, it is very important to know where your soil and fill are coming from.
The prolific invader boasts several different advantages which allows it to outcompete co-occurring plant species. Established stands of knotweed emerge in early spring meaning that they beat other plant species in the race for key resources like space, sunlight, water, and nutrients. Once mature, the plant’s thick crown and zigzagging branches create a dense thicket preventing other plants from growing. Established stands are so dense that their broad leaves and woody stocks can reduce the amount of light that reaches the ground by up to 90%. By the end of its growing season, a thick mat of dead knotweed will accumulate, further preventing co-occurring plant species from emerging the next spring.
The presence of Japanese knotweed in an ecosystem can greatly reduce biodiversity. Not only does it outcompete native plant species, but it also forces the relocation of insects and small animals such as amphibians, reptiles, birds, and mammals that rely on native plant species for food and habitat.
wikiHow. (2021). https://www.wikihow.life/Identify-Knotweed
While removing Japanese knotweed can be extremely difficult (near impossible sometimes), especially for the home gardener, this does not mean that there is nothing that you can do! You can learn how to identify Japanese Knotweed to avoid accidental spread when you encounter it by inspecting, cleaning, and removing any mud, seeds, or plant materials from clothing, pets, vehicles, or machinery like mowers. You should always avoid planting it, educate others not to plant it, and avoid using soil in areas where Japanese knotweed is present. If you see an infestation, capture a picture of it and submit it to iNaturalist: https://inaturalist.ca/!
To enter our giveaway, post a picture of a local infestation, post it, tag us, and use #25watershedmoments.
Anderson, H. (2012). Invasive Japanese Knotweed (Fallopia japonica (Houtt.)) Best Management Practices in Ontario. Ontario Invasive Plant Council, Peterborough, ON. https://www.ontarioinvasiveplants.ca/wp-content/uploads/2016/06/OIPC_BMP_JapaneseKnotweed.pdf
OFAH/OMNRF Invading Species Awareness Program. (2021). Japanese Knotweed. Retrieved on February 8, 2024, from: www.invadingspecies.com.
Subramanian, S. (2023). The war on Japanese knotweed. The Guardian. https://www.theguardian.com/environment/2023/may/16/the-war-on-japanese-knotweed
wikiHow. (2021). 3 Ways to Identify Knotweed. Retrieved on February 8, 2024, from: https://www.wikihow.life/Identify-Knotweed