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Japanese knotweed
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Japanese knotweed
| Common name: | Japanese knotweed |
| Scientific name: | Fallopia japonica |
| Management programme: | Organism of interest |
Report this pest!
If you have seen or suspect the presence of this pest we need to know. Please report it.
Contact Otago Regional Council on 0800 474 082 or biosecurity@orc.govt.nz
Japanese knotweed, also known as Asiatic knotweed, grows rapidly from an extensive fleshy underground root system, forming dense thickets that can live for a long time. They exclude other desirable species and prevent native seedlings from establishing.
Knotweed is a very hardy plant and difficult to control. Originally from Japan, knotweed is a very serious invasive pest plant in many parts of New Zealand. It grows to form dense thickets which expand rapidly. It can choke waterways as the thickets completely replace any other vegetation.
- Size: A perennial shrub that forms dense thickets with numerous cane-like stems up to 2 metres high. The stems are hollow when mature and have a zig-zag appearance between each leaf node. The stems are hairless with a reddish tinge.
- Leaves: Leaves are oval and pointed, alternating, and up to 25 cm long.
- Flowers/seeds: Flowers are small and white and are clustered along short branches between December and April, followed by small (2.5–3 mm long) angled glossy brown seeds.
- Root system: They propagate from rhizomes (underground shoots) as well as from seeds.
- Habitat: Includes shrubland, urban areas, waste areas, and waterways.
Knotweed flowering
Japanese knotweed
Japanese knotweed
Japanese knotweed
Japanese knotweed
Japanese knotweed
Knotweed flowers
Knotweed leaves
Japanese knotweed is easiest to spot when its small white flowers are out in summer and autumn (December–April).
There are no rules for landowners in Otago regarding Japanese knotweed. Under Otago’s pest plan, it is only classified as an Organism of Interest, with sites being recorded for possible opportunities in the future. Landowners/occupiers are encouraged to report Japanese knotweed on their properties or sightings using the reporting tool at orc.govt.nz/reportpests
Physical control:
Dig out small patches and dispose at landfill or burn.
Chemical control:
- Cut the stump near the ground and paste year-round using a suitable herbicide gel containing either glyphosate, metsulfuron-methyl or triclopyr.
- Inject the stem year-round with metsulfuron-methyl.
- Spray foliage when the plant is actively growing from spring to autumn with a penetrant plus glyphosate, metsulfuron-methyl or triclopyr.
- Spray in spring, but a follow-up may be required in February or March.
- Check for regrowth every three months for at least two years and re-treat as necessary.
Caution
Japanese knotweed can spread by soil movement, garden waste and equipment such as diggers and farm machinery. When disturbed, it can break up easily into small fragments that can easily regrow. Take special care not to disturb it or transport it to new sites.
When using any herbicide or pesticide PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.
Disclaimer: Mention of product trade names does not endorse these products nor imply criticism of similar products not mentioned. The Otago Regional Council does not give any warranty that the information is accurate or complete or that it is suitable for all circumstances.
