Knotweed Complex
Knotweed Complex Flowers
Knotweed Complex Stems

Polygonanceae or Buckwheat Family
Polygonum cuspidatum, sachalinense & polystachyum

Knotweed Complex Species:
Japanese, Giant, and Himalayan Knotweed.
Growth Habit: Herbaceous, shrub-like perennial that grows to heights in excess of 10 feet.
Leaves: Six inches long, and 3 to 4 inches wide, broadly oval to somewhat triangular, mostly pointed at the tip, and are alternate on the stems.
Stems: Smooth (bamboo-like), stout, and swollen at the joints where the leaf joins the stem. Stems are hollow, but may be water-filled depending upon soil moisture levels and where it is growing.
Flowers: Small, pale greenish-white flowers.
Roots: Rhizomes may extend 30 feet in length. Buds along the length of rhizomes may develop into new stems depending upon environmental and cultural conditions. Digging around the base of established plants encourages new vegetative buds to develop along the rhizome system.
SEEDS: Seeds are triangular, shiny, very small about 1/10 inches long. Seeds are not viable outside its native range of Asia.
REPRODUCES: Spreads by sprouts from rhizomes of established plants and from sprouts arising from stems that have been severed from the mother plant.
HABITAT: Riparian areas, upland sites, irrigation ditches, and road-rights-of-way.

Handpulling is only effective on small infestations if done at least twice a month or as new shoots emerge. Since knotweed can re-establish from root or stem fragments, all parts of the plant that are removed should be placed on a tarp and be allowed to completely dry out before being burned.
Mowing: Mowing has the potential to be effective at reducing the size of infestations if done consistently and persistently over many years. Mowing or cutting should occur at least three times a year with the last mowing occurring before plants start to lose their leaves prior to winter. Care should be taken to ensure all stem fragments are removed from the site and from the mower and treated like those removed by handpulling.
Biological Control: N/A
Grazing: Knotweed is palatable for almost all forms of livestock, but grazing will not kill the plants. Grazing could potentially reduce the size and vigor of knotweed infestations if it is heavy and consistent.
Herbicides: Care should be taken when knotweed infestations occur in wetland or riparian areas to use appropriately labeled herbicides. Cutting an infestation and waiting for fresh re-growth prior to herbicide treatment may increase effectiveness. The following herbicides have been labelled for control of knotweed. Always consult product labels and read them carefully to ensure correct species/land management usage and chemical application.

Trade Name: Active Ingredient:  Rate:  Efficacy:   Comments: 
 Habitat imazapyr  2 qts/acre  most effective if plants are cut and 12" of re-growth allowed before treatment  Can cause injury to desirable trees and shrubs if root systems extend into treatment area 
 Rodeo glyphosate  2.5-8% solution most effective if plants are cut and 12" of re-growth allowed before treatment    Non-selective and must be applied very carefully if you are to prevent damage to non-target species


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