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Bathurst burr (Xanthium spinosum)

Bathurst burr is a significant weed of pastures, rangelands, crops and horticultural land in Australia. Its hooked burrs contaminate wool, and its seedlings are poisonous to livestock, particularly horses and pigs.

Key facts

Type: Weed, herb.

Native to: South America.

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

Other names: Spiny Cocklebur, Spiny Burweed, Spiny Clotbur, Daggerweed.

Best time to act: Look for seedlings during spring and summer germination flushes, and treat plants before burrs form.

Identification

  • This annual, multi-stemmed herb grows up to 1 metre tall, with downy stems.
  • At the base of each leaf are usually one or two rigid, yellowish, three-pronged spines, 7 to 25 millimetres long.
  • Leaves are usually three-lobed, narrow, dark green with prominent whitish veins above, and whitish or silvery and felted below.
  • The flowers are green to yellowish green, and the plant produces oval burrs about 10 to 12 millimetres long.
  • Burrs have numerous hooked spines and short beaks.
  • Look-alike: Noogoora burr (Xanthium strumarium) has similar hooked burrs, but lacks Bathurst burr's three-pronged stem spines and has broader adult leaves.
  • Look-alike: Cockleburr (Xanthium ambrosioides) has smaller, generally narrower leaves and smaller fruits, usually without beaks.

Where it grows

It occurs in all Australian states and territories, especially on disturbed, fertile soils in exposed temperate areas, including sheep camps, watercourses, dam banks and floodplains.

Why it matters

  • It is a weed of pastures, rangelands, summer crops and horticultural crops, including cotton, maize, peas, potatoes, soybeans, sugarcane and grapes.
  • Hooked burrs contaminate wool, making fleeces harder to process, reducing their value and causing problems for shearers.
  • Seedlings, especially the cotyledons, are poisonous to livestock, particularly horses and pigs; older plants are not eaten.
  • It invades native grassland, grassy woodland, riparian vegetation, freshwater wetlands and other sites, and contact may cause dermatitis in some people.

How it spreads

  • Hooked burrs attach readily to livestock and clothing and can be carried in mud and soil.
  • Burrs float on water and are carried along watercourses and across floodplains.
  • The plant is also dispersed by people, machinery and agricultural produce.

Control options

  • Target seed production: use registered herbicides, particularly on young plants, and spray before burrs form; combining treatment with competitive pasture is recommended.
  • For small infestations, hoe or grub and chip plants; hand removal is not recommended because of the sharp spines.
  • Repeated cultivation can control seedlings on arable land, and slashing should be done before burrs form; follow-up may be needed after summer seedling flushes.
  • Prevent seeding for at least four to six years and address reinfestation sources; do not dump burr-bearing plants, but gather and burn them.

Hygiene and washdown

  • Check clothing, livestock, machinery and other equipment for hooked burrs before moving them, as burrs attach readily and can spread with machinery and agricultural produce.
  • Avoid moving mud or soil containing burrs, and take care around watercourses where burrs can float and spread.
  • 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: Regionally controlled / restricted weed (varies by region). 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: 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: Declared pest. It is a declared pest throughout the ACT.

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
  • Northern Territory: Territory Parks and Wildlife Conservation Act 1976 (NT), administered by NT Department of Lands, Planning and Environment

Sources