Sharp rush
Spiny rush
Juncaceae - Juncus acutus
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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 is sexually mature from about two years and can live up to 30 years.  Seed germination is reduced by darkness.  Soil disturbance is likely to facilitate establishment.  Germination rate and speed decrease with increasing salinity. Long-lived seed bank.

Invasive overseas, particularly competitive at lower salinity levels. Less competitive in water-logged soils. Vectors of spread: Seed is dispersed by water, contaminated machinery and soil movement.  Vegetative spread via rhizomes. 

Control Methods

Physical control:
Thick rhizomes & roots make physical control difficult. Herbicide treatments best after heavy rain has washed salt from plant.

Firstly, dig out all roots & rhizomes. Then either:
  • Weed wipe spring-summer (300ml glyphosate+2ml penetrant/1L).
  • Knapsack spray spring-summer (100ml glyphosate + 20ml penetrant/10L).

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

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