Japanese knotweed

Japanese knotweed

Fact Sheet


Latin Name: Fallopia Japonica

Origin:  Asia

Physical Description: It has hollow, smooth, purple to green coloured stems up to 2.5cm in diameter. The hollow jointed stems have reddish-brown solid nodes surrounded by a papery sheath (stipule). Plants grow in clumps, with stems reaching up to 3m in height.  Alternate leaves are oval to triangular with a pointed tip and flat base with a long stalk. They are typically 10-17 cm long and 7-10 cm wide. Flowers are small, white-green and situated at end of the stem and in the leaf axils. Rhizomes are dark brown, with a bright orange interior. The underground root systems (rhizomes) account for two thirds of the pants total mass. These rhizomes can extend more than 2 m deep and 14-18 m in length, and can spread outwards at a rate of about 50 cm/year in optimal conditions.

Habitat: Found in areas that have moist soil and full or partial sun. It can survive very harsh conditions with a pH range of 3.0-8.5 and the ability to survive extreme heavy metal and salt pollution and areas with low available nitrogen. It is often found in riparian areas as well as in spoil piles, derelict land, road and railway right of ways and gardens. Its growth and abundance are reduced in shady sites making it unable to successfully dominate in forests.

Impacts:  Knotweeds have significant social, economic and environmental impacts. They compete with native plants, destroying habitat and reducing biodiversity. Their roots cause stream bank erosion, as well as damage to building foundations, pavement, bridges and other structures. These plants can also impede sight lines along road ways, posing public safety issues.

Reproduction:  Most plants are female with male sterile flowers therefor reproduction is primarily vegetative. Plants typically regenerate from small stem and root fragments.

Rhizome fragments weighing as little as 0.7 g are capable of regenerating into a new plant. Research has shown that Japanese knotweed can reproduce through hybridization with other knotweed species, such as Giant knotweed (Fallopia sachalinensis).

Management Options

Mechanical: mechanical control is not recommended as plants will continue to reproduce reproduces through remaining root and stem fragments. Digging small infestations may be effective if all of the plant parts, including the entire root system, is removed.

Chemical: The following active ingredients can control Japanese knotweed: Aminopyralid, Glyphosate and Imazapyr. For available products, contact your local agri-supply store. Prior to any herbicide application, read and follow the label instructions.

Biological: Aphalara itadori, a sapsucking psyllid, is under going research for use in BC however is not yet available for distribution.

Additional Resources: 

Best Management Practices for Knotweed Species in the Metro Vancouver Region

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