Purple Nut Grass

(Cyperus rotundus)

purple nut grass

Status of purple nut grass in Tasmania

  • Purple nut grass is a declared weed in Tasmania under the Tasmanian Weed Management Act 1999. The importation, sale and distribution of purple nut grass are prohibited in Tasmania.
  • The legal responsibilities of landholders and other stakeholders in dealing with purple nut grass are laid out in the Purple Nut Grass Statutory Weed Management Plan.

What does purple nut grass look like?

  • Purple nut grass is an erect perennial (long-lived) sedge growing to 50 cm high. The stems are smooth, unjointed and triangular in cross section. The leaves are glossy dark green, V-shaped in cross section, with small serrations on the margin and with a prominent mid-vein. The flowers are a cluster of reddish/purplish brown spikelets which are carried on 3 to 9 flower stems. The seeds are black, brown, olive or gray, ovoid-shaped and beaked. The root is an extensive system of rhizomes (underground stems), tubers (also called nuts) which are purplish in colour, and basal bulbs (swellings of the stem base just below the soil surface).
  • Growth of new plants from tubers occurs in spring as temperatures rise. Flower stems form in late spring and flowers are produced in summer. All above-ground growth dies back in autumn.
  • Purple nut grass spreads mainly via tubers, as seed viability is low. A single tuber can give rise to over 600 plants, and a cubic metre of soil may contain over 50 000 tubers! Tubers can remain dormant in the soil until dormancy is broken by the rhizome being cut into pieces. Tubers can be spread by cultivation equipment and in contaminated soil, gravel or water.
  • Purple nut grass is very similar to yellow nut grass (C. esculentus) but is distinguished by its brown to purple flowers.
Purple nut grass purple nut grass
Images top & above: purple nut grass, © Luigi Rignanese.

Impacts of purple nut grass

  • Purple nut grass is a serious weed of a wide range of crops, and dense infestations can reduce crop yields by over 75%.

Where does purple nut grass occur?

  • Purple nut grass is a pan-tropical species of doubtful origin which has naturalised widely in tropical and warm-temperate regions. In Australia, purple nut grass has naturalised in all mainland States and Territories.
  • Purple nut grass has not managed to establish in Tasmania.

What you need to do

  • If you locate purple nut grass anywhere in Tasmania, or if you find a plant that you think could be purple nut grass, immediately contact Biosecurity Tasmania on 03 6165 3777 to report this weed.

See also
Purple Nut Grass Statutory Weed Management Plan
Weed Links and Resources

Other useful links
Pest Genie

Important Disclaimer
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