Weedbusters

A tall, nasty grass

Location: Northland (particularly the Northern Wairoa River), Auckland, Waikato, Wellington Distinctive features: leaves rustle loudly in the wind, very tall plant (up to 2-3m high), 60cm-long purple or red-brown flowers in November-december. Dense, mat-forming perennial that grows thick rhizomes, up to 5m long, and fibrous roots. Harsh, papery, dull grey-green leaves (2-3cm wide) are straight, then taper to a point. Why is it weedy: spreads quickly and widely in wet and dry areas, forming dense, long-lived stands on land and water that smother other plants. Extremely tolerant of damage, grazing, cold or heat, wind, fire, different soil types, moderate shade and moderate salinity. How does it spread: mostly by seed, and when rhizome fragments move, eg when a river is in flood, on farm machinery, when caught on boats/boat trailers, possibly by birds.

How to kill 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 plants, if there is a small number. Dispose of rhizomes and seedheads at a refuse transfer station, or burn them.

2. Weed wipe (September-april): for small sites, especially over water. Gallant (333ml/l + 50 ml crop oil).

3. Spray: Gallant NF(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.