Himalayan Knotweed

Himalayan Knotweed

Scientific name: Polygonum polystachyum (Persicaria wallichii)

Common name: Himalayan knotweed

Description: Himalayan knotweed is one of several invasive knotweeds in Clatsop County. It is an aggressive, bamboo-like perennial that spreads by underground rhizomes, often forming dense, monocultured thickets. It was originally imported from the Asian continent as an ornamental screen or hedge plant. In North America, this plant is not suppressed by natural competitors and is thus able to thrive in a wide range of ecological settings. What does it look like? Knotweed has green or reddish stems, bright green leaves with smooth edges, spikes of small, white flowers in late summer, dies off during the winter months, and can grow in dense vigorous stands up to 12 feet tall. Leaf shape varies according to knotweed variety.

Impact: Knotweed invades stream banks, displaces native vegetation, destroys critical fish and wildlife habitat, reduces riverside recreational value, and can damage foundations, yards, and roads. Due to its vigorous spreading growth habit and its ability to reproduce from severed root segments, large patches are difficult to treat and eradicate. Most commonly knotweed reproduces through root or rhizome spread, thus flooding and contaminated fill material all increase the spread of knotweed. Clatsop SWCD is actively treating knotweed populations in the county! If you suspect knotweed is on your property, please contact our office at 503-325-4571.

Source: KingCounty.gov

For more information, please visit the Noxious Weed resources at KingCounty.gov: http://www.kingcounty.gov/services/environment/animals-and-plants/noxious-weeds/weed-identification/invasive-knotweeds/himalayan-knotweed.aspx