Weedbusters

Working together to protect New Zealand

  • Weedbusters
    • Who are Weedbusters?
  • What Are Weeds?
    • Weed List
    • Controlling Weeds
    • Disposing of Weed Waste
    • Banned Plants
  • Get Involved
    • Become a Weedbuster
    • Weedbusters Near You
    • Weed Quiz
    • 2-Minute Film Challenge Previous Winners
    • Funding Sources
  • Articles & Events
    • Articles
    • Events
    • Submit an Article
    • Submit an Event
  • Resources
    • How To…
    • Free Weedbusting Guide
    • Plant Me Instead Booklets
    • Weed Control Handbook
    • Display Panels
    • Media-Ready Material
    • Useful Links
  • Contact Us
You Are Here:
  1. Home
  2. What Are Weeds?
  3. Weed List
  4. Weed Information Sheet
What Are Weeds?

Weed Information Sheet

  • Weed List
  • Controlling Weeds
  • Disposing of Weed Waste
  • Banned Plants

Popular Links

  • Find That Weed!
  • Try the Weed Quiz
  • Read the Latest Articles
  • Weedbusters Near You
  • Weedbuster Events

Browse Weeds by Alphabet

a b c d e f g h i j k l m n o p q r s t u v w x y z

Asiatic knotweed

Botanical Name

Fallopia japonica

Family

Polygonaceae (dock)

Also known as

Reynoutria japonica, Japanese knotweed, R. japonica cv ‘Compacta’, Polygonum reynoutria, P. cuspidatum

Where is it originally from?

Asia

What does it look like?

Many-stemmed, thicket-forming perennial shrub (<1-2 m high) forming roots with rhizomes and numerous, zigzagging, hairless, bluish to reddish stems (<15 mm diameter) that are woody at the base. Ovalish, pointed leaves (8-23 x 5-17 cm) with less than 14 pairs of lateral veins are bluish below, and on dark crimson stalks. White flowers (<2.5 mm long) in densely-hairy, branched hanging clusters (<6 cm long, Dec-Apr) are followed by glossy brown nuts (3 mm).

Are there any similar species?

Fallopia sachalinensis

Why is it weedy?

Grows rapidly and extensively from rhizomes and multiple stems. Produces relatively long-lived and well dispersed seed, and tolerates wet to moderately dry conditions, and warm to cold temperatures, but is intolerant of shade.

How does it spread?

Seed and rhizomes are spread by soil and water movement.

What damage does it do?

Forms dense, long-lived thickets, excludes other species and prevents native seedlings establishing.

Which habitats is it likely to invade?

Shrubland and areas around waterways.

What can I do to get rid of it?

1. Dig out small patches (all year round): Dispose of at refuse transfer station or burn.
2. Weed mat: leave for 6 months minimum. Dig or spray surviving shoots.
3. Stump swab (all year round): glyphosate (250ml/L) or metsulfuron-methyl 600g/kg (5g/L) or triclopyr 600 EC (200ml/L).
4. Stem injection (all year round): 5ml metsulfuron-methyl 600g/kg (50g/L) per stem.
5. Spray (spring-autumn): glyphosate (200ml/10L) or metsulfuron-methyl 600g/kg (5g/L) or a product containing 100g picloram+300g triclopyr/L (6ml/L) or triclopyr 600 EC (6ml/L). Add penetrant.

What can I do to stop it coming back?

Stem fragments and rhizomes resprout. Seeds germinate in bared areas. Difficult to control. Follow up 3-monthly for at least two years until eliminated.

Images

Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Trevor James
Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Trevor James
Photo: Trevor James
Photo: Trevor James
Photo: Trevor James
Photo: Trevor James
Photo: Trevor James
Photo: Trevor James
Photo: Trevor James
Photo: Trevor James
Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Carolyn Lewis
Photo: Carolyn Lewis

Download PDF Information Sheet

Browse/Search Weeds

Weedbusters

  • Who are Weedbusters?

What Are Weeds?

  • Weed List
  • Controlling Weeds
  • Disposing of Weed Waste
  • Banned Plants

Get Involved

  • Become a Weedbuster
  • Weedbusters Near You
  • Weed Quiz
  • 2-Minute Film Challenge Previous Winners
  • Funding Sources

Articles & Events

  • Articles
  • Events
  • Submit an Article
  • Submit an Event

Resources

  • How To…
  • Free Weedbusting Guide
  • Plant Me Instead Booklets
  • Weed Control Handbook
  • Display Panels
  • Media-Ready Material
  • Useful Links
  • Home
  • Contact Us

© 2023 • Website by RS

  • Home
  • Weedbusters
    • Who are Weedbusters?
  • What Are Weeds?
    • Weed List
    • Controlling Weeds
      • Controlling Pest Shrubs & Trees
      • Controlling Pest Vines
      • Controlling Pest Herbs & Ground Covers
      • Controlling Pest Grasses
      • Controlling Pest Aquatic Weeds
    • Disposing of Weed Waste
    • Banned Plants
  • Get Involved
    • Become a Weedbuster
    • Weedbusters Near You
    • Weed Quiz
    • 2-Minute Film Challenge Previous Winners
    • Funding Sources
  • Articles & Events
    • Articles
    • Events
    • Submit an Article
      • Using Citizen Science for yellow flag iris data collection
    • Submit an Event
      • Kumeu River weed walk
  • Resources
    • How To…
      • Raise Weeds Awareness
      • Organise a Weedbusters Event
      • Put Together a Press Release
    • Free Weedbusting Guide
    • Plant Me Instead Booklets
    • Weed Control Handbook
    • Display Panels
    • Media-Ready Material
    • Useful Links
  • Contact Us
  • Find us on Facebook