Japanese Knotweed Control Guide

Do's and don'ts of Japanese knotweed control

Japanese knotweed leaves

Do's

  • Get in early - large infestations can be very difficult to eradicate;
  • Remove and carefully dispose of all rhizome material: small broken pieces of Japanese knotweed left in the ground or in the removed soil can grow into new plants;
  • Check an infestation regularly over several years in case of regrowth from remnants of the root system; and
  • Commit to follow up control measures each year for up to 3 years to eradicate the plant.

Don'ts

  • Don't leave new infestations to establish - get in early and eradicate;
  • Don't let it seed;
  • Don't rely on one attempt at eradication - the plant will grow back from the persistent rhizome;
  • Don't leave fragments of rhizome in the soil: they will regrow into new plants;
  • Don't dump removed material or removed soil, as this can spread the plant to new areas; and
  • Don't compost or mulch root material as rhizome fragments can reshoot.

Spread of Japanese knotweed

  • In Tasmania Japanese knotweed appears to have only reproduced asexually by regeneration of rhizome fragments. However, spread by seed also occurs in the plant's native range in Japan.
  • Japanese knotweed rhizomes are able to regrow from small fragments. Rhizome fragments can be spread in contaminated soil and garden waste. Plants have been known to regenerate from fragments buried up to 1 metre deep.
  • The long lived rhizomes can spread at a rate of 2 metres a year, leading to rapid expansion of an existing colony.
  • See the Washdown Guidelines for Weed and Disease Control for detailed information on how to wash-down equipment and personnel to reduce the chance of spreading Japanese knotweed.
Physical removal
  • Small plants can be pulled by hand or dug up. Make sure that all root and rhizome material is removed. The use of a sieve to get all root material out is recommended.
  • Larger clumps can be controlled through repetitive cutting of the stems near the soil surface and immediate application of herbicide (see Chemical Control, below). Several cuttings and herbicide applications will be needed to kill the plant. Cutting back on its own is not enough as the rhizome will survive.
  • The dug-up plant and root material must be disposed of carefully to avoid spreading the weed. All material should be removed and dried out and then burnt in a safe manner.

Chemical control

  • There are herbicides registered for foliar and 'cut and paint' application to Japanese knotweed in Tasmania. See Herbicides for Japanese Knotweed Control for more information.
  • Repeat applications are required within the growing season to capture all new growth. If sprayed with a foliar herbicide you will need to cut back material after approximately three to four weeks to see new shoots and get access to them.
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