Manchurian rice grass
Botanical Name
Zizania latifolia
Family
Poaceae (grass)
Also known as
Manchurian wild rice
Where is it originally from?
China
What does it look like?
Dense, mat-forming perennial (<2-3 m) with rhizomes (2-3cm diameter) up to 5 m long and fibrous roots. Harsh, papery, dull grey-green leaves (2-3 cm wide) are straight, up to 2.5 m long, have a stout midrib, taper to a point, and rustle loudly in the wind. From November to December a purplish or red-brown flowerhead (40-60 cm long) is produced.
Are there any similar species?
Raupo is similar, but has 1-2 m leaves that are thick and spongy, 2 cm wide, have no midrib, and twist upwards, it has a bullrush-style seedhead. Flax leaves are much wider, smoother, thicker and shinier than Z. latifolia and have a balsa-like flowering stalk.
Why is it weedy?
Seeds and rhizomes fragments spread rapidly and widely in wet or dry areas, and it forms dense, long-lived stands on land and water margins, overtopping other riparian species. Extremely tolerant of damage, grazing, cold or heat, wind, fire, different soil types, moderate shade and moderate salinity.
How does it spread?
Rhizomes spread outwards slowly, but more rapid spread comes from seeds and rhizome fragments being moved by water, livestock, machinery, clothing, and possibly by birds. Road graders, soil movement, dumped vegetation, contaminated diggers, farm machinery, eel nets, boats and trailers all spread seed and rhizome fragments into new catchments, lowland pasture, roadsides, water tables, drains and farm dams.
What damage does it do?
Forms permanent stands in water margins and dry land of nothing but Zizania latifolia, replacing all other species. Causes silt to accumulate, altering water systems, causing flooding and destroying habitat for aquatic fauna and flora.
Which habitats is it likely to invade?
All fresh or moderate-saline waterbodies and margins, wetlands, damp ground and fernland.
What can I do to get rid of it?
Always begin control work at the top of the catchment. Resource consent is usually required for spraying over water - contact your regional council for more information on this.
1. Dig out only very small sites. Dispose of rhizomes and seedheads at a refuse transfer station, or burn them.
2. Spray: 520g/L haloxyfop-P-methyl (10ml/L + 50ml crop oil). Initial spray September-April. Follow up 6-8 monthly (not in winter) before regrowth reaches 1m, to prevent rhizome recovery.
What can I do to stop it coming back?
Rhizomes persist for years and can recover after spraying, and seed bank may reinfest bared areas, so ongoing control is important. To prevent problems with rhizome disposal, it is better to kill rice grass standing using an overall spray application: budget for 50-70% regrowth after first 1-2 treatments, 10% thereafter. Usually need 5-10 treatments over 6-8 years for eradication.
