Biosecurity Spotters logo

Lesser burr-grass (Cenchrus spinifex)

Spiny burr-grass is an introduced weed found across mainland Australia, especially in eastern Australia. Its sharp burrs can injure people and animals, contaminate produce and hay, and reduce the value of wool and hides.

Key facts

Type: Weed, grass.

Native to: North and Central America.

Established in: QLD, NSW, VIC, SA, WA.

Other names: Innocent weed, Gentle Annie, American burr grass, Lesser burrgrass.

Best time to act: Look for germinating plants mainly in spring and early summer, and control them before they set seed; burrs are produced from December to April.

Identification

  • It is an upright tufted or spreading grass, usually up to about 60 cm tall, with occasional plants reaching 80 cm.
  • Its narrow leaves are flat-folded or rolled inwards, mostly smooth and hairless, and can grow to 20 cm long.
  • The spike-like seed-head has clusters of spiny burrs, usually densely packed and sometimes partly enclosed by the uppermost leaf sheath.
  • Mature burrs are straw-coloured or brown, 3–10 mm across, and have usually 10–40 sharp spines.
  • The smooth, flattened, egg-shaped seeds are hidden inside the burrs.
  • Look-alike: Cenchrus longispinus is very similar, but its burrs usually have 40–70 spines in total.
  • Look-alike: Mossman River grass (Cenchrus echinatus) has unstalked burrs with one row of larger flattened spines; buffel grass (Cenchrus ciliaris) has no spiny burrs.

Where it grows

In Australia it occurs mainly in eastern Australia, particularly sub-coastal northern New South Wales and south-eastern Queensland, and grows in disturbed sites, waste areas, roadsides, pastures and cultivated land, often on sandy soils.

Why it matters

  • Burrs can injure people and dogs, and spines can cause mouth swellings and ulcers in stock or puncture animals' skin.
  • Burrs tangled in wool lower its value and slow shearing, while spines can reduce the value of hides.
  • Burrs can contaminate dried fruit crops and lucerne hay, and make work in irrigated crops more difficult.
  • The plant also grows on urban footpaths, bare streetscapes and recreation grounds.

How it spreads

  • The plant reproduces by seeds held inside spiny burrs, which commonly attach to animals, vehicles and clothing.
  • Burrs can also spread in contaminated agricultural produce and on machinery, and may be dispersed by water.
  • Seeds may remain viable in burrs for at least five years, and some can stay dormant and germinate later.

Control options

  • Prevent seed production: cultivate before seed formation, preferably while plants are seedlings, and repeat cultivation to kill later seedlings.
  • Physical removal can be used, but larger plants are difficult to turn over completely; heavy sheep grazing can prevent seedlings where practical.
  • Well-managed pastures can out-compete the grass and prevent it becoming established.
  • Herbicides applied to actively growing plants can be effective; repeat treatments may be needed where germination occurs several times in a season, and only use registered herbicides according to their labels.

Hygiene and washdown

  • Clean vehicles and machinery to remove burrs and reduce spread.
  • Check clothing, equipment and materials such as agricultural produce, soil and gravel for attached or contaminating burrs.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Regional priority in 2 of 11 regions. Regional priority weed in Central Tablelands, Western. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Declared plant. Depending on the declaration, it can be an offence to move it on public roads or sell it, and landowners may be required to control it on their land.
  • Western Australia: Not listed. Not found in the Western Australian Organism List. Check with DPIRD before moving or keeping it.
  • Tasmania: Declared weed. Property managers are required by law to control declared weeds, and their import and sale are prohibited.
  • Northern Territory: Not declared. Not on the NT A to Z weed list, and Weeds Australia does not list it as declared in the NT. Check the NT declared weeds list before moving or planting it.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)
  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development
  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria
  • South Australia: Landscape South Australia Act 2019 (SA), administered by the regional landscape board
  • Western Australia: Biosecurity and Agriculture Management Act 2007 (WA), administered by the WA Department of Primary Industries and Regional Development

Sources