Knotweeds

 

Latin name:

Polygonum spp.

Native to:

Asia

REGIONALLY NOXIOUS

Regional Distribution:
Knotweeds in the Columbia-Shuswap are commonly found around human inhabited areas as they are generally introduced as garden ornamentals before they get out of control and expand into surrounding areas. Knotweeds are often found at dump sites as they have the remarkable ability to take root and grow from a single node along the stem.

Description:
There are three main kinds of knotweeds found in the Columbia Shuswap region:
Japanese knotweed
Bohemian knotweed
Giant knotweed

Knotweeds are perennial invasive plants with aggressive growth. They can reach an impressive 3-4 meters in height. The young shoots of knotweed are similar in form to bamboo canes. Knotweeds excel at regenerating from suckers as well as nodes along the stem. If you are not sure which type of Knotweed you are dealing with check out the Knotweed Identification Key published by the Ministry of Forests, Lands and Natural Resource Operations.

Control:
The best control is prevention and early action. Do not plant knotweed in your garden! There are alternative ornamentals that can be grown in their place. Once established knotweeds are very difficult to control and can cause damage to human infrastructure and degrade riparian habitat. One of the only effective control measures against knotweed is targeted herbicide. This can take the form of foliar application (herbicide applied directly to the leaves).

Once established, knotweed is extremely difficult to eradicate.  It can re-grow after cutting, burning, or insufficient treatment with herbicide.  Small cuttings of the stem or roots can grow a new plant, proper disposal at your local landfill is imperative to reducing further introductions – do not put in compost or yard waste piles.

More information about knotweed control options can be found at Knot On My PropertySea To Sky Invasive Species Council Control Methods and ISCBC TIPS sheet

Key Recommendations:

  • Control knotweed on your property.
  • Carefully dispose of knotweed garden waste at your local landfill or transfer station. Knotweed must be double bagged and the landfill attendant must be notified of its contents prior to dumping. DO NOT COMPOST !!
  • Avoid planting invasive species. Alternative species and more information regarding this plant can be found on our website: http://columbiashuswapinvasives.org/resources-for-gardeners/

Scary facts:
Knotweeds can cause extensive damage to infrastructure and have been seen breaking through concrete foundations and asphalt along roadsides. The rhizomes of knotweed are incredibly resistant to cold weather and can survive to temperature below -35 degrees Celsius.