Cyperus rotundus

Nutgrass

Also known as:

Purple nut sedge

Family: Cyperaceae

Origin: India

Nutgrass with immature seed heads on a white table.
From India, this Cyperus looks similar to the native Cyperus but is very weedy. This hardy plant is not easily controlled by chemical means and can become herbicide resistant.

Regional Pest Management Plan (RPMP) status

  • Whole region — Sustained control
  • Hauraki Gulf Controlled Area Notice pest

View more about the RPMP statuses

General description

Erect perennial rush < 35 cm tall. Rhizomes are extensive and tuberous. Stems are triangular. Flowers are borne in simple open umbels with few rays. Nuts are small and rarely reach maturity.

What you need to know

To help protect our environment:

  • You must not breed, distribute, release or sell nutgrass within the Auckland region.
  • You must not plant nutgrass within the Auckland region, unless you are transferring an existing plant on your land to another location within the boundaries of the same property.
  • You must destroy any nutgrass on land that you occupy if it has been planted in breach of the above rules and you are directed to do so by an authorised person.

Habitats

Pasture, roadsides, wetlands, riparian margins, coastal areas, cropland, urban habitats.

Dispersal

Low production of viable seed. Vegetative spread from rhizomes and tubers, dispersed by water. Human-mediated dispersal through movement of contaminated soil.

Impact on environment

Potential to outcompete native species in wetlands, riparian margins and coastal areas. Reduces crop yields. May hybridise with the closely related C. ustulatus.

Control

Site Management

Follow up treated areas 3 times per year. Encourage natural regeneration of native plants or replant treated areas where possible after 2-3 treatments to establish dense ground cover and minimise reinvasion.

Recommended approaches

Physical control

Method: Dig out.

Plant parts requiring disposal: Tubers and rhizomes.

Disposal options: Remove to greenwaste or landfill if practical.

Biocontrol

Biocontrol is currently not available for this species.

Community agrichemical control recommendations

No qualifications: Foliar spray with 200ml glyphosate green per 10L of water.

Basic Growsafe certified: Foliar spray with 200ml glyphosate green per 10L of water and 20ml penetrant.

Certified Handler/Experienced agrichemical user: Follow up treated areas 3 times per year. Encourage natural regeneration of native plants or replant treated areas where possible after 2-3 treatments to establish dense ground cover and minimise reinvasion.

Caution: When using any herbicide or pesticide please read the label thoroughly to ensure that all instructions and safety requirements are followed.

Nutgrass colony with mature flower heads.
Plants grow tubers and rhizomes which can survive in many conditions and be spread by spreading soil. Can outcompete our native plants in wetland and boggy areas.
A row of immature Nutgrass plants with roots on table.
The seeds that are produced have low viability so the nutgrass spreds mainly by humans moving soil. The roots are very strong making the plant hard to hand pull in many situations.
Photo credit: Forest and Kim Starr