Japanese knotweed is a perennial plant that can tower over 10 feet tall creating an impenetrable wall along streambanks. It’s large leaves are 3-4”wide and 4-6” long and spade-shaped or heart-shaped.
How It Spreads
Once it is established adjacent to a stream it can quickly spread downstream. It spreads vegetatively, meaning that if swept away by spring flows and deposited downstream one small piece of stalk or root can result in a new infestation. We have mostly witnessed this occurring on rivers and streams whose streambanks are not shaded by trees. We also find it in areas where soil contaminated with rhizomes has been used for streambank or bridge repair.
Impacts to Rivers
Large infestations of Japanese knotweed on rivers and streams can lead to increased bank erosion, sedimentation, and exacerbated flooding. It also makes lousy habitat for our native birds and other fauna that rely upon our river corridors for food, shelter, and migration. Not to mention, it can make accessing a river or stream difficult for us people as well.