Clinton County Invasive Species Project: Japanese Knotweed Inventory

What is Knotweed?

Japanese Knotweed is a robust, bamboo-like perennial plant native to Asia. Common names include Mexican or Japanese bamboo, elephant ear and fleece flower. It is a noxious weed that is fast growing and extremely aggressive. It invades along rivers and roads, but is also found in backyards, forests, parks, and farms.

Our Project Description & Goal

Clinton County Soil and Water Conservation District is involved in a multiyear 2 phase invasive species project to inventory and eradicate high priority areas of Japanese Knotweed.

Phase 1

In 2019 we will focus on identifying areas that Japanese Knotweed has infested our county. Infested sites will be documented with photos, a written description of the size of the area, and other valuable information. High priority sites will include areas near streams or other bodies of water as well as areas where knotweed is causing maintenance issues for local highway departments and NYS-DOT.    This will take some coordination with local municipalities and highway departments

Phase 2

Phase two starts in 2020 and we will determine the necessary steps to treat the high priority areas of Knotweed infestation. The ultimate goal is to eradicate all high priority sites within the county thus promoting native species growth.

Identifying Japanese Knotweed

It is a rhizomatous (produces underground stems) perennial plant with distinctive, branching, hollow, bamboo-like stems, covered in purple speckles and can grow from 3-15 feet tall.

The leaves of the mature plant are 3 to 6 inches in length with a flat base and pointed tip. They are arranged on arching stems in a zig-zag pattern.

The plant flowers in late summer, August to September, with small creamy-white flowers hanging in clusters from the leaf axils (point at which the leaf joins with the stem).

The underground rhizomes are thick and woody with a knotty appearance and when broken reveal a bright orange-colored center. The horizontal roots can reach lengths of 65 feet or more.

The plant develops small winged fruit seeds which are triangular, shiny, and very small (about 1/10 inch long). Japanese Knotweed spreads primarily by seed (transported by wind, water, animals, and humans).

Why is it a problem?

Knotweed spreads rapidly, forming dense thickets that overwhelms and shades out native vegetation. This threatens the diversity of our natural ecosystem, reduces species diversity, and negatively impacts wildlife habitat.

Limits recreational access and obstructing scenic views.

Because the ground under knotweed tends to have very little other growth, it can create bank erosion problems, clog small waterways and trout streams. It reduces food sources for wildlife and lower nutrient input into streams systems.

The aggressive growth of the Knotweed can also damage yards and structures such as foundation and roads.

What to Do if You See Japanese Knotweed:


Use this website  to try to make a positive identification. Many plants look similar to Japanese Knotweed.


Entire plant, stem, leaves, flower, seed. High resolution preferred. We’ll need them to confirm identification.


Call our office: 518-561-4616 ext 3 or email photos and location to