Latin Name: Polygonum spp, Fallopia spp.

Physical Description: These perennial forb species are originally from eastern Asia. They were introduced to Europe and North America as ornamentals in the early 1800s and are listed as one of the worst 100 invasive plant species by the World Conservation Union. Bohemian knotweed is an aggressive and adaptable hybrid between Japanese and giant knotweeds and is probably the most common of the invasive knotweeds in British Columbia, although the other three species are also causing problems.

All four species have a similar appearance and are difficult to distinguish in the field. Himalayan knotweed has pinkish-white flowers while the other three species have greenish-white flowers. All four species have hollow reddish bamboo-like stems, large broad leaves, and rhizomatous roots. Giant knotweed can grow to 6 m, Japanese knotweed to 4 m, and Himalayan to 3 m tall.

Type: Perennial forb

Habitat & Impacts: These species grow in a wide range of open sites but do not tolerate shade. It is most common in moist low-lying sites but can also tolerate extreme heat and drought. The knotweeds form dense stands and may virtually eliminate other vegetation on a site.

Method of Spread: The main form of reproduction is vegetative with new shoots forming from underground rhizomes or root fragments.

Mechanical: Hand pulling or mowing prior to seed set with repeated treatments after the initial cutting.

Chemical: Chemical treatments consist of: Picloram, 2, 4-D, aminopyralid, and Glyphosate, and applied before flower production.

Biological: Twelve different biocontrol agents have been used in British Columbia with good establishment and reduction in plant vigour. Success at removing plants and reducing densities in infestations is limited at this time to localized areas in the southern areas of the Province. Agapeta zoegana (Root feed moth), Cyphocleonus achates (Root feeding weevil), Larinus minutus and obtusus (seed feeding weevils), and Metzneria paueipunctella, (Seed feeding moth) have been released within the Cariboo Chilcotin.

CCCIPC Priority & Treatment Strategy: Priority 1 (new invader) in Nazko, Chilcotin & Central Cariboo, Priority 2 (containment) in all other regions. All sites west of the Fraser River will be eradicated. Sites east of the Fraser River will be managed on a site-specific basis to reduce the rate of spread and density of existing infestations along the main corridors near Hwy 97 and infested lands. Future containment lines may be considered in some heavily infested areas. A large percentage of the sites on the inventory map are monitoring only as the weed has been effectively controlled.

Local Level: Hand pulling small infestations and chemicals where appropriate.

Landscape Level: Chemical treatments, hand pulling, and biocontrol releases and monitoring effectiveness.