Jan Samanek, State Phytosanitary Administration, Bugwood.org

Japanese Knotweed (Fallopia japonica)

Often called "Bamboo". Rhizomatous perennial with jointed stems growing to 3 m (10 ft) tall. Leaves are alternate on the stem, nearly heart-shaped, dark green on top and paler green on the underside. Flowers are greenish-white, white or pink approximately 2 mm long that grow from leaf axils and appear August to September.


Habitat and Ecology

Prefers moist areas at low elevations but can tolerate flood and seasonal drought conditions. Commonly found in riparian areas, ditches, wetlands and private gardens.


Dense stands will crowd out native vegetation very aggressively. New shoots can grow up to 10cm in one day. It especially threatens river and streams degrading fish and wildlife habitat. When dormant, dries and can be a fire hazard.


Very difficult to control so a combination of methods is recommended. Often chemicals cannot be used because of the proximity of the infestations to water. Stem injections have been used as well as brushing biodegradable herbicide on cut stems. If the patch is under 300 stems, cutting and digging can be an options. Further covering of the area with plastic a mulch is also another option. Proper collection and disposal of vegetation is essential because stem portions and roots can propagate new plants. LRISS recommends that a certified and knowledgeable professional/contractor be hired for removal projects because of the high risk that this plant can spread as a result of improper treatment and disposal.


Forest Service: Beware these Alien Weeds… Japanese Knotweed (Polygonum cuspidatum ) and Giant Knotweed (P. sachalinense ).