The Mission of the Yellowstone County Weed Department is to assist the public, private, and other government agencies to manage and control existing noxious weed infestations as well as to prevent new invasive species from infesting Yellowstone County.

Knotweed Complex - Japanese, Giant, and Himalayan, not Prostrate KnotweedPolygonum cuspidatum, sachalinense & polystachyum

Photo from Montana Weed Control Association

Rosette

Stem

Leaf

Bloom

Plant

Seed

Photos from Montana Weed Control Association

Video Supplied By Montana Weed Control Association

Attribute	Description
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