Coastal Invasive Species Committee

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Japanese Knotweed

cow knotweed

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Fallopia japonica

CONTAIN

Japanese knotweed is a tall shrub with bamboo-like stems. It has been planted throughout South and Central Vancouver Island and the Gulf Islands as a garden ornamental but quickly spreads to form dense thickets in a variety of habitats, including dry roadsides and moist stream banks. Small patches can quickly spread into large areas, leaving little room for native species to grow.

These plants can be identified by their tall (>3 metres), bamboo-like stem structure, leaves that are flat at the base with a pointed tip and small white flowers that bloom in late summer.

Family: Polygonaceae (Buckwheat).

Other Scientific Names: Fallopia japonica, Polygonum cuspidatum Reynoutria japonica.

Other Common Names: Fleeceflower, Japanese bamboo, American bamboo, Mexican bamboo, huzhang, Hancock's curse, elephant ears, donkey rhubarb.

Origin: Asia.

Growth Form / Reproduction: Deciduous perennial. Spread mainly vegetatively from rhizomes but will produce viable seed if Bohemian knotweed is nearby.

Legal Status: Forest and Range Practices Act, Community Charters Act.

Impacts:
Agricultural: Knotweeds can be eaten by grazing animals.
Ecological: Dense stands may compete with and replace native vegetation.
Human: Knotweeds have been used as landscape ornamentals.

Habitat: Adapted to moist conditions and to a variety of soil types; generally shade intolerant. Disturbed sites, roadsides, streams banks, ditches, wetlands, riparian areas, railroad and utility corridors

Status and Distribution: Widespread in all Regional Districts except Capital where it is common. Most common in CDFmm, CWHxm and CWHvm but present in CWHvh and CWHdm.

Management Strategy: Eradicate new infestation where feasible. Contain or control existing populations. Once established, knotweeds are extremely difficult to control; the rhizomes extend meters beyond the clones and they can regenerate from tiny fragments. Digging or hand-pulling can result in plants re-sprouting. Cutting, mowing, grazing and foliar herbicides can reduce top growth but repeated treatments are required for long-term control.

 

Additional Information:

Understanding & Controlling Invasive Knotweeds in BC by Jeff Hallworth

Invasive Plant Council of BC - TIPS Sheets

BC Ministry of Agriculture- Field Guide to Noxious Weeds

Sensitive Habitat Inventory Mapping, Knotweed ID guide

King County, USA, Best Management Practices for Knotweed