Department Header For Noxious Weed Division
Yellowstone County, Montana
Noxious Weed
Weed Information Contact Department

Knotweed Complex - Japanese, Giant, and Himalayan, not Prostrate Knotweed
(Polygonum cuspidatum, sachalinense & polystachyum)


Knotweed Complex

Photo from Weeds of the West, revised edition.

Knotweed Complex Rosetta

Knotweed Complex Stem

Knotweed Complex Leaf

Knotweed Complex Bloom

Knotweed Complex Plant

Knotweed Complex Seed

Photos from Montana Weed Control Association


Growth Habit: Perennial, 4 to 9 feet in height

Leaves: Leaves are short-petioled, broadly ovate, 2 to 6 inches long and about two-thirds as wide, narrowed to a point.

Stem: Stems are stout, woody, reddish-brown, die back at the end of the season.

Flower: Flowers are greenish white to cream, borne in large plume-like clusters at ends of stems and in leaf axils.

Roots: Creeping Rhizomes, roots can spread 20 feet from the plant and go down as deep as 7 feet into the soil.

Seeds: Fruit is 3-sided, black and shiny.

Reproduction: By rhizomes and seed.

Habitat: Escaped ornamental, found along roadsides,waste areas, ditch banks, and pastures.

Biological Controls:

Herbicides: Glyphosate, Trichlopyr, Imazapyr


Video Supplied By Ravalli County Weed District