Knotweed (several species)
Knotweeds are classified as noxious weeds. They spread quickly, particularly along rivers and steams where they can out-compete native plants and destroy habitat for spawning fish.
These type of weeds have massive root systems, sometimes as deep as 9 feet! They grow in dense stands up to a whole 12 feet tall!
NOTE: If they are left unchecked, knotweed will steadily take over river and stream banks, as well as beaches.
There are four genetically related species of non-native knotweeds that are classified as Class B noxious weeds on Washington’s Noxious Weed List.
Japanese Giant Bohemian Himalayan
What is ‘Class B‘?
A ‘class B‘ listing means that these weeds are either absent from or limited in distribution in some portions of the state, but very abundant in other areas. The management approach for Class B weeds is to contain the plants where they are already widespread and prevent their spread into new areas.
What is the issue?
Knotweeds displace normal riparian vegetation, disrupting the food chain by altering the timing and quality of leaf litter introduced along riparian corridors. This in turn changes nutrient runoff, soil composition, and the source of food available to invertebrates that form the base of the aquatic food web. Knotweed stands apparently accelerate bank erosion, thereby, damaging salmon and fish habitat.
Where are knotweeds in this region?
Knotweeds are found throughout the Puget System basin.
What is being done?
The Department of Agriculture works with local noxious weed control boards, state agencies, not-for-profit organizations and tribes to survey for and treat infestations.