Sharp rush
Spiny rush
Juncaceae - Juncus acutus

What does it look like?

Sharp rush is a perennial spiny rush forming dense stiff clumps up to 1m tall.  Stems are cylindrical and sharp tipped, and rhizomes woody.  Clumped green/brown flower heads occur near the end of each stem in summer.  Red/brown/orange fruit capsules are present in autumn, with approximately 200 seeds per head.

Preferred habitats include the upper reaches of salt marshes, mud flats and ephemeral dune wetlands, plus neighbouring damp scrub, lake margins, damp pasture and roadsides. It favours damp sandy soils without standing water, but tolerates both seasonally dry soils and standing water.

Present in coastal areas of Northland, Auckland, Waikato and Manawatu.  The worst infestations in Northland are around the Whangaroa Harbour and on the Pouto Peninsula, Kaipara Harbour, but it is also present in other areas.  It is not known to be present at any of the high value dune lakes, but is present in some wetlands.

Why is it a problem?

Sharp rush out-competes other coastal plants as it is quick to mature and produce seed, with a long-lived seed bank. It's seeds are also very easily dispersed by wind, water, contaminated machinery and soil movement. It can also spread vegetatively via it's rhizomes. Sharp rush is also unpleasant for animals & humans, with the spikes very sharp to the touch, hence the name 'sharp rush'.

Control Methods

Physical control

The sharp tips of this plant and it's thick rhizomes & roots make physical control difficult. However it is possible to do this if thick clothing is worn to prevent injury. A spade may be used to leverage the plant out from the soil/sand. Once the mass is removed, dig surrounding soil/sand to check for remaining roots or rhizomes as these can regrow.

Herbicide control:
Firstly, dig out all roots & rhizomes, then either:

  1. 'Weed-wipe' spring-summer with 300mL glyphosate + 2mL penetrant / 1L water.
  2. Knapsack spray spring-summer with 100mL glyphosate + 20mL penetrant / 10L water. 

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