Environment

Manchurian rice grass

Manchurian rice grass.Manchurian rice grass.

Common name:
Manchurian rice grass, Manchurian wild rice

 

Scientific name:
Zizania latifolia

 

Regional classification:
Service delivery - our Council will only arrange eradication for small outlying infestations

 

National classification:
National Pest Plant Accord – banned from being sold, propagated or distributed

Description

Manchurian rice grass is a dense mat-forming perennial grass species that grows 2-3 metres high and sometimes up to 5 metres.  It has deep roots and thick rhizomes that spread widely.

 

Seed head:

  • 40-60cm long
  • purplish or red-brown in colour
  • rough to the touch and contains many seeds
  • seeds are produced in November-December

Leaves:

  • long and straight
  • dull grey-green
  • 2-3cm wide with stout midrib
  • harsh, thin and papery
  • tapers to a sharp point

The leaves may bend over at the top, and make a loud, rustling noise in the wind.  Rice grass is often confused with raupo and flax, but raupo has shorter softer leaves and flax leaves are much smoother and shiny.

Why is it a problem?

Manchurian rice grass grows 2-5 metres high.Manchurian rice grass grows 2-5 metres high.

Rice grass seed germinates very quickly and is carried by water movement. Birds also help to spread seed.

 

Rhizomes spread outwards and broken fragments are carried by water to new sites.  The most significant method of spread is through contaminated diggers and farm machinery.

 

Eel nets, boats and trailers also spread rice grass fragments.

 

Rice grass forms pure stands, excluding all other vegetation. As well as invading waterways, it also replaces pasture, rendering farmland and crops almost worthless.  The abrasive leaves cause woody tongue and ill thrift in livestock.

 

The dense vegetation also creates major flooding problems by blocking floodways. Rhizomes also penetrate and destroy stopbanks, causing further flooding.

 

Native plant and fish habitat is also destroyed by rice grass.

What can I do?

Because of the plant’s deep and extensive rhizome system, control by digger is largely ineffective.  Root and rhizome fragments will quickly resprout.

 

Cattle will eat young foliage but do not thrive on it and cannot check rhizome spread.  Small infestations can be controlled by mowing and then covering completely with heavy polythene for two years or more.  The cover needs to extend at least five metres beyond the rice grass to prevent rhizome regrowth. This method is seldom practical.

 

Herbicide control remains the only workable option in most cases. However, the use of herbicides near waterways is severely restricted, and in most cases a resource consent from the Northland Regional Council will be required.

 

Where possible the maintenance of a dense pasture sward will suppress ricegrass. This can be achieved through drainage, fertiliser, grazing and the encouragement of vigorous grass species.

 

Regular mowing or slashing, followed by grazing pressure, will limit the plants impact on grazing land. 

Your responsibility

Manchurian rice grass is a pest plant in Northland and cannot legally be propagated or distributed in any way, including being carried by machinery.

 

It is probably the worst aquatic weed in Northland. The long term goal is to contain and progressively control the plant within the major infestation area in Dargaville and eradicate all other infestations in Northland.

Recommended control suggestions

Resource consent from the Northland Regional Council will be necessary for use of chemicals near water. Please contact us for advice. The applicator must hold the relevant qualifications and adhere to manufacturers’ guidelines.

 

Recommended approaches:

  1. Dig out very small sites.
  2. Weed wipe small sites (terrestial sites only) Sep - Apr (300ml haloxyfop + 5ml crop oil/1L).
    Spray (terrestial sites) Sep - Apr (100ml haloxyfop + 50ml crop oil/10L). Follow up 6-8 monthly (not in winter) before regrowth reaches 1m, to prevent rhizome recovery.

Disposal:

 

Better to kill in situ as disposal of rhizomes a major challenge; crush or dry them, then burn or soak in haloxyfop.

Caution: When using any herbicide PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.

More information

For further information or control advice please contact one of our Biosecurity Officers at the Northland Regional Council on 0800 002 004:

  • Whangarei: Ken Massey
  • Dargaville: Peter Joynt
  • Kaitaia: Doug Foster
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