Invasive knotweed is an aggressive species known for displacing native vegetation and degrading habitat. As a class A noxious weed, removal is required. Stems are hollow canes, and the leaves are large and spade shaped. It spreads by rhizomes and seeds. Even a small piece that breaks off can travel and re-root. 

If the patch of knotweeds is relatively small, manual digging can be effective. For larger patches, herbicide injections are required by a licensed applicator. Dispose in trash bags. DO NOT COMPOST. Visit kingcounty.gov for more information. 

(Image credit: Washington Noxious Weed Control Board)