About Manchurian wild rice
Manchurian wild rice is a giant, perennial grass which produces rhizomes (underground root-like stems) and grows up to 4 m tall. It has harsh, erect, dull-grey-green leaves (2 cm to 3 cm wide) up to 2.5 m long that have a stout midrib and taper to a point. Unlike raupō, which can look similar, it remains green over winter. From November to December, a purplish or red-brown flower head (40 cm to 60 cm long) is produced.
Why we don't want Manchurian wild rice in New Zealand
Manchurian wild rice is a highly invasive grass that forms dense, long-lived stands on land and water margins, overtopping other river-bank species. The grass was accidentally introduced in contaminated soil (used as ballast) to the Northern Wairoa River around 1900.
Land becomes more flood-prone where Manchurian wild rice is present because the extensive rhizome system damages stop banks and thick stands block irrigation and drainage channels. This weed also displaces pasture species on low-lying land, reducing productivity.
Where Manchurian wild rice has been found in NZ
Manchurian wild rice is only known to occur in the Northland, Auckland, Waikato, and Greater Wellington regions. It grows in areas next to rivers, lakes, and drains, in swamps and on low-lying farmland.
Manchurian wild rice control and eradication
Manchurian wild rice is one of the species being eradicated through the National Interest Pest Responses programme. The programme is focused on eradication from the Auckland, Waikato, and Greater Wellington regions. In Northland, where infestations cover about 500 hectares, the aim is to keep infestations around the northern Wairoa River (the Containment Zone) from spreading further and eliminate all populations outside of this zone. We are also looking into new tools to control the heaviest infestations in the Containment Zone so that we can completely eradicate Manchurian wild rice from New Zealand in the long-term.
Infestations are regularly sprayed with herbicides until no further regrowth occurs, which can take several years to achieve. A site can be declared free of this pest after 10 consecutive years with no regrowth.
Biosecurity New Zealand works closely with the regional councils and other organisations to eradicate Manchurian wild rice from New Zealand.
National Interest Pest Responses programme
How the weed spreads
Spread is mainly by rhizome fragments on excavators and farm machinery. Water movement, eel nets, boats and trailers also spread rhizome fragments. To prevent the spread, all potentially contaminated items should be checked, and all rhizome material removed before leaving the site.
What to do if you find Manchurian wild rice
Manchurian wild rice is an Unwanted Organism under the Biosecurity Act (1993). Propagation, spread, display, and sale are all prohibited. It is also a Notifiable Organism, which means you must report all sightings to the Ministry for Primary Industries.
If you find this plant in the Northland, Auckland, Waikato, or Greater Wellington regions contact the local regional council. If you find it outside these regions:
- freephone our pest and disease hotline on 0800 809 966
- don’t touch the plants or try to remove them
- take photos and leave the plants so they can be treated or removed safely without spreading the pest further.
Manchurian wild rice – Fact sheet [PDF, 1.2 MB]
Manchurian wild rice – Flyer [PDF, 1.3 MB]
