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

 

Photo from Weeds of the West, revised edition.

Rosetta	Stem	Leaf
Bloom	Plant	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