Photo-PSU Extension

Where are they from?

This plant was introduced in the late 1800s from East Asia to stabilize stream banks and as an ornamental plant.

Why are they so harmful?

Knotweed is a very aggressive plant that can gain control of wetlands, stream buffers, forest and field edges. The root system increases the plants’ ability to disperse, these systems are interconnected horizontal roots or “rhizomes.” These horizontal roots can fragment and any piece of these roots can form a new plant. Also, if stems are cut without removing the root system they are fully capable of growing back. They are very difficult to get rid of even after multiple attempts. Large stands of knotweed can decrease plant and animal biodiversity, damage property, and degrade water quality.

How can I identify this plant?

Use identifying apps like Seek by iNaturalist (On both Apple and Google Play stores).

When unable to use phones, remembering what the plant looks like from pictures and descriptions is best. Stems of this plant resemble bamboo having a hollow stem, and where leaves are attached there are red or purple nodes. Leaves are large, heart-shaped, and have a square base. Flowers emerge in late summer and come in clusters with five petals that are white or pale green.

Where can I learn more?

Information Page by PSU Extension-- https://extension.psu.edu/japanese-knotweed

Factsheet by PSU extension--- https://plantscience.psu.edu/research/projects/vegetative-management/publications/crep-weed-management-factsheets/4-managing-japanese-knotweed

Accurate Identification-- https://www.youtube.com/watch?v=xauIJAa1zXQ