Navua sedge

Native to tropical Africa, Navua sedge is a vigorous, grass-like, perennial plant.

It has been introduced to a number of countries, including Sri Lanka, Malaysia, Fiji, Vanuatu, Samoa, Tahiti and the Solomon Islands. In Australia, Navua sedge was first found growing on Cairns footpaths in 1979 and is now more broadly distributed in north Queensland.

Navua sedge competes strongly with pasture and other plants for nutrients, light and moisture.

Navua sedge is not a prohibited or restricted invasive plant under the Biosecurity Act 2014.

Scientific name

Cyperus aromaticus

Description

  • Vigorous, grass-like perennial sedge, generally 30-70cm tall, occasionally reaching 2m.
  • Continuously growing underground stem produces shoots at regular intervals along its length, which can then develop an extensive, shallow, fibrous root system.
  • Leaves are 5cm long, 3cm wide, in drooping clusters at base of stem.
  • Flowers are white, at apex of triangular stalk.
  • Seeds are brown to black, egg-shaped, with hook at one end.

Habitat

  • Prefers areas with annual rainfall exceeding 2,500mm and no distinct dry season.
  • In areas with substantially less rain and distinct dry season, generally restricted to damp, low-lying pastures or disturbed areas.

Distribution

  • Found in scattered populations in north Queensland and South East Queensland.

Life cycle

  • Seedlings develop quickly and flower 10 weeks after emerging. At flowering, underground stem produces new shoot. New shoot then grows as seedling did, producing flower 10 weeks after seedling emerges and producing another new shoot from underground stem.
  • Seeds can germinate at any time of year but highest germination occurs when temperatures alternate between 15˚C and 25˚C. Seeds also require exposure to light for germination.
  • Seed heads on each shoot generally produce about 250 seeds each.
  • Longevity of seeds has not been determined.

Impacts

Environmental

  • Competes strongly for nutrients, light and moisture.

Economic

  • Invades and replaces pastures.
  • Problem in sugar cane where crop is light with poor canopy cover.
  • Forms dense stands that smother tropical pasture species.

How it is spread

  • Spread occurs through normal extension of rhizome system, by seed and by dispersal of viable rhizome fragments during cultivation.
  • Seed can be dispersed in animal and bird faeces, and in mud on hooves, pelts, footwear and machinery.

Control

Physical control

  • Dig out with spade and turn entire plant over, exposing root system and completely covering all aerial parts of plant.
  • For large infestations, may be possible to bring underground roots to surface by discing and allowing them to dry out. Effectiveness will depend on weather, because damp conditions are likely to encourage considerable regrowth.

Mechanical control

  • Mechanical control of large infestations has been achieved in Fiji using heavy rollers at intervals of 8-12 weeks to repeatedly break stems at ground level and allow grass to out-compete sedge. This is impractical in hilly country.
  • Mechanical control methods are generally not a long-term solution and require repeated applications.

Herbicide control

Biological control

  • No known biological control agents.

Mechanical control

  • Mechanical control of large infestations has been achieved in Fiji using heavy rollers at intervals of 8-12 weeks to repeatedly break stems at ground level and allow grass to out-compete sedge. This is impractical in hilly country.
  • Mechanical control methods are generally not a long-term solution and require repeated applications.

Herbicide control

Biological control

  • No known biological control agents.

Legal requirements

  • Navua sedge is not a prohibited or restricted invasive plant under the Biosecurity Act 2014. However, by law, everyone has a general biosecurity obligation (GBO) to take reasonable and practical steps to minimise the risks associated with invasive plants and animals under their control.
  • Local governments must have a biosecurity plan that covers invasive plants and animals in their area. This plan may include actions to be taken on certain species. Some of these actions may be required under local laws. Contact your local government for more information.

Further information