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L'înformâtion et les sèrvices publyis pouor I'Île dé Jèrri

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Japanese knotweed

Report Japanese knotweed sightings using the PlantTracker app

​You can help us gather data on where Japanese knotweed is found in Jersey by reporting and sending photos of plants you find.

You can download PlantTracker, a free app, to record and submit photos of the plants and their location. This information is then sent directly to the Environment Department.

After we confirm it is knotweed, your sighting will be plotted on a map showing the invasive plant's progress.

Free Plant Tracker app

Japanese knotweed

Japanese knotweed is a tall, vigorously growing perennial plant which originates from Japan. It is aggressive and can colonise most habitats including:

  • stream banks
  • woodlands grasslands
  • coastal areas
  • road verges
  • gardens
  • waste ground

What Japanese knotweed looks like

Japanese knotweed is easily recognisable at all stages of its growth, and has characteristic hollow bamboo-like stems which are usually pale green and purple in its mature state. The plant produces small white flowers in late summer, and its leaves are arranged in a zigzag pattern up stem which enables the plant to utilise maximum sunlight.

Damage caused by Japanese knotweed

The plant is not currently listed as an injurious weed under the Weeds (Jersey) Law, so there is no legal obligation for a landowner or occupier to prevent it from spreading. However, it is strongly recommended that this plant is at least controlled wherever it is found to minimize future spread across the Island.

Japanese knotweed:

  • can re-grow from tiny cut fragments of the plant; maintenance by mowing, strimming or flailing the plant may help, not hinder, its spread
  • shoots are able to push through asphalt, damaging
    • pavements
    • car parks
    • patios
    • roads
    • houses
  • rhizomes (underground creeping stems, capable of producing new plants) are capable of
    • penetrating foundations of walls
    • penetrating land drainage works
    • lifting interlocking concrete blocks
  • is a very successful competitor. The foliage forms a dense canopy which restricts the growth of ground flora and the establishment of other plant species

The best methods to controlling Japanese knotweed

There are a variety of options available to control the plant, including

  • hand pulling
  • cutting
  • chemical treatment
  • grazing
  • deep burial

Whichever control method is used, killing the extensive rhizome system is essential if lasting control of Japanese knotweed is to be achieved. This may mean that the management programme will take a number of years to be effective. It is important to realise that there is no quick solution for the control of Japanese knotweed.

Japanese knotweed leaflet

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