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Californian burr (Xanthium strumarium)

Noogoora burr is a major weed of disturbed ground, floodplains and agricultural land in Australia, particularly in Queensland, the Northern Territory and New South Wales. Its burrs contaminate wool, while seedlings are poisonous to livestock and the plant competes with pasture and crops.

Key facts

Type: Weed, herb.

Native to: North America.

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

Other names: Cockleburr, Clotbur, Large Cockleburr.

Best time to act: Look for plants during warm-weather growth and treat them while young and actively growing; burrs form from February to May.

Identification

  • It is a single- or multi-stemmed herb that can grow up to 2 metres tall; its hairy stems have no spines.
  • The broad, ovate to triangular leaves are usually 50 to 150 millimetres long and wide, with 3 or 5 lobes and toothed margins.
  • Leaves are darker green on top, prominently 3-veined, and have a stalk 20 to 120 millimetres long.
  • The burrs are 15 to 25 millimetres long, covered in hooked spines, and have two longer, stout, straight spines or beaks.
  • Separate male and female flowers occur on the same plant; male flowers are cream or creamy green, and female flower heads are yellowish green to brown.
  • Look-alike: Bathurst burr (Xanthium spinosum) has three long, sharp spines on the stem at the base of each leaf, while Noogoora burr is spineless.
  • Look-alike: Bathurst burr has narrow adult leaves, 8 to 22 millimetres wide, and burrs with small or no beaks; Noogoora burr has broader leaves, usually 50 to 150 millimetres wide, and two distinct beaks on its burrs.

Where it grows

It occurs across mainland Australia, especially in low-lying areas subject to inundation, along rivers and creeks, and on flats after late spring or summer flooding.

Why it matters

  • Burrs contaminate wool, making fleeces harder to work with and reducing their value.
  • Seedlings are poisonous to livestock, particularly horses and pigs.
  • Rapid growth and an extensive root system make it a serious competitor in pasture and cropping.
  • Dense thickets can exclude understorey plants and threaten wetland plant biodiversity; contact may also cause dermatitis, and pollen may cause hay fever.

How it spreads

  • Hooked burrs attach to livestock, clothing and other fibrous material.
  • Burrs also spread in mud and soil, road gravel, and road-making equipment.
  • Air cavities around the seeds help burrs float, so they spread readily along waterways and across floodplains.

Control options

  • Hand hoeing or chipping is practical only in small or sparsely populated areas and is labour intensive.
  • Sheep can graze plants before flowering and after the cotyledon leaves have dried, but check that no seedlings are present because they could kill animals.
  • Use registered herbicides suited to the situation when plants are young and actively growing; plants under severe moisture or weather stress are difficult to kill.
  • The rust fungus Puccinia xanthii is established in Australia and can reduce plant growth and burr production; its effectiveness depends on warm, humid conditions.

Hygiene and washdown

  • Remove hooked burrs from clothing and other fibrous gear so they are not carried to new sites.
  • Avoid moving contaminated mud, soil or road gravel, and check road-making equipment for burrs before it leaves an infested area.
  • 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: Not a priority weed. Not a state or regional priority weed in NSW. 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: Declared pest (C2, C3). C2 Eradication: present in limited areas and targeted for eradication. C3 Management: landholders must manage it to reduce its impact and stop it spreading.
  • Tasmania: Declared weed. Property managers are required by law to control declared weeds, and their import and sale are prohibited.
  • Northern Territory: Declared weed, Class B. Class B: growth and spread must be controlled. All declared weeds are also Class C, so they must not be brought into the NT.
  • 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