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Invasive, Exotic Plants of the Southeast


Japanese Knotweed

Japanese Knotweed

Common Name: Japanese Knotweed

Scientific Name: Polygonum cuspidatum

Identification: Japanese Knotweed is a perennial shrub reaching 4 to 8 feet in height.  Leaves are 4 to 6 inches long and pointed.  The stems are reddish-brown and freely branched.  The white flowers are on drooping panicles and appear from August to November.  The fruits are small, brown, and triangular in shape and mature from September to January.

Ecology: Japanese Knotweed forms dense stands and aggressively outcompetes native vegetation.  This invasive shrub has vigorous rhizomes and colonizes roadsides and riparian areas.  It spreads by water dispersed seeds and through transport by humans.

Plant Control: Apply a glyphosate herbicide in combination with cutting.  If the Japanese Knotweed is in an aquatic habitat, you will need to use a product such as Rodeo or AquaNeat. Glyphosate by itself will not harm aquatic habitats but surfactant-loaded glyphosate formulations like Roundup can be highly toxic to amphibians, frogs, and other aquatic fauna. Cut the stems off above the waterline and treat the outer cut surface (the stems are hollow) with a plain glyphosate product such as Accord or Rodeo (53.8%). Monitor re-growth and re-treat as needed to achieve control. 

Alternative Native Species: Virginia Willow (Itea virginica), Sweet Pepperbush (Clethra alnifolia)

When using herbicides remember to follow label-recommendations.  Any mention of trade, products, or firm names is for descriptive purposes only and does not imply endorsement by North Carolina State University.

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