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Spiny burr-grass (Cenchrus longispinus)

Its sharp, clingy burrs can injure people and animals, contaminate produce and wool, and add to farm costs. It can spread rapidly and form dense infestations, and is difficult and expensive to manage in some areas.

Key facts

Type: Weed, grass.

Native to: North and Central America.

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

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

Best time to act: Look for germination mostly in spring and early summer, and control plants before they set burrs, which are produced from December to April.

Identification

  • An upright or spreading, sparse grass, usually up to 60 cm tall but sometimes reaching 90 cm.
  • Its narrow leaf blades are 3–20 cm long and 3–8 mm wide, and are mostly hairless.
  • The flower head is a spike 3–7 cm long.
  • Burrs are 3–12 mm across and usually bear 40–70 sharp spines, each 3.5–7 mm long.
  • Young burrs are reddish or purplish-green, turning straw-coloured or brown as they mature.
  • Look-alike: Spiny burrgrass (Cenchrus spinifex, also referred to as C. incertus) has similar rows of flattened spines, but usually has 8–25 spines per burr rather than 40–70.
  • Look-alike: Mossman River grass (Cenchrus echinatus) has burrs without stalks and only one row of larger flattened spines, while buffel grass (Cenchrus ciliaris) has seed heads without spiny burrs.

Where it grows

In Australia it occurs mainly in sub-coastal south-eastern areas, especially south-eastern South Australia, north-western Victoria and south-western New South Wales, and grows in disturbed sites such as roadsides, pastures and waste areas, often on sandy, well-drained soils.

Why it matters

  • Sharp burrs can injure people and dogs, and spines can injure stock, including causing mouth swellings and ulcers.
  • Burrs tangle in wool, reducing its value and slowing shearing, and can damage hides by puncturing animal skin.
  • Burrs can contaminate dried fruit and lucerne hay, reducing the value of hay.
  • The weed can spread rapidly and form dense infestations, making it difficult and expensive to manage.

How it spreads

  • Seeds are contained in spiny burrs that commonly attach to animals, vehicles and clothing.
  • Burrs can also be dispersed by water and in contaminated agricultural produce.
  • Some seeds can remain viable inside burrs for up to five years.

Control options

  • Preventing seed set is key; cultivate before seed formation, preferably while plants are seedlings, and repeat cultivation to control later seedlings.
  • Heavy sheep grazing can prevent seedlings, and well-managed pastures can exclude the weed.
  • Registered herbicides applied to actively growing plants can be effective; repeat treatments may be needed where germination occurs several times in a season.
  • In dryland areas control can be difficult because seeds remain viable in burrs, and herbicide control of broad-acre infestations can be prohibitively expensive.

Hygiene and washdown

  • Clean machinery and vehicles to reduce spread, and check clothing and gear for burrs because they can attach to them.
  • 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 West, Western. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Regionally prohibited / regionally controlled / restricted weed (varies by region). Where it is regionally prohibited, landowners must take all reasonable steps to eradicate it on their land. Where it is regionally controlled, landowners must take all reasonable steps to prevent its growth and spread on their land. Where it is a restricted weed, trade in it (including the plant, its seed or contaminated material) is prohibited.
  • 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
  • Australian Capital Territory: Biosecurity Act 2023 (ACT), administered by ACT Biosecurity
  • 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
  • Northern Territory: Territory Parks and Wildlife Conservation Act 1976 (NT), administered by NT Department of Lands, Planning and Environment

Sources