Japanese knotweed

What is Japanese knotweed?

(Fallopia japonica)

Japanese knotweed leavesGeneric Weed Distribution Map
  • Japanese knotweed is an environmental weed.
  • Japanese knotweed is a declared weed in Tasmania under the Tasmanian Weed Management Act 1999. The importation, sale and distribution of Japanese knotweed are prohibited in Tasmania.

How to identify Japanese knotweed

  • Japanese knotweed is a fast growing, hollow-stemmed and semi-woody perennial plant that forms dense leafy thickets. Plants are commonly 2-3 metres high and may reach 5 metres in height.
  • Japanese knotweed stems are stiff, hollow and bamboo-like, becoming tough, woody and speckled with age. The stems arise at intervals from rhizomes or underground stems. Leaves measure up to 12 cm long and 10 cm wide and have a pointed tip.
  • Japanese knotweed flowers from December to February. Flowers are small and white and borne on slender branched spikes. Fruit is a three-angled papery sheath that covers a single shiny black seed. Most of the foliage dies back over autumn.
  • Roots are coarse, perennial rhizomes which are yellow when cut. They grow up to three metres deep and spread many metres from the parent plant.
Japanese Knotweed Infestation
Image top right: Japanese knotweed leaves (Chris Moore)
Image above: Japanese knotweed infestation (Chris Moore)

Japanese knotweed in Tasmania

  • Japanese knotweed occurs in northern Tasmania, mostly in garden situations (see map). Japanese knotweed has not been recorded in the north-west or in the south of Tasmania.
  • Japanese knotweed is a significant weed in riparian (river-side) areas, disturbed coastal habitats, wetlands and roadsides, where it displaces other vegetation by shading and root competition. Japanese knotweed dies back over winter, leaving bare soils open to erosion.
  • The rhizomes (underground stems) of Japanese knotweed can spread under walls, pavements and patios and cause damage to roads and buildings.

What is the legal status of Japanese knotweed in your area?

Detailed management and control guidelines for Japanese knotweed can be found in the Japanese Knotweed Control Guide. Refer also to Herbicides for Japanese Knotweed Control. For further information see DPIPWE's Weed Links and Resources.

See also
Japanese Knotweed Control Guide
Herbicides for Japanese Knotweed Control
Japanese Knotwood Statutory Management Plan
Weed Links and Resources

Other useful links

Pest Genie
APVMA


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