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Nodding thistle (Carduus nutans)

In Australian pastures, nodding thistle can form dense, spiny patches that out-compete desirable pasture plants and reduce carrying capacity. It is difficult to control because it produces many seeds, has a persistent seed bank and can germinate whenever moisture is available.

Key facts

Type: Weed, herb.

Native to: Europe, northern Africa, Asia Minor and Asia.

Established in: QLD, NSW, ACT, VIC, TAS.

Other names: Musk thistle.

Best time to act: Look for rosettes in autumn and treat seedlings or small rosettes; spring treatment when the first buds are obvious has also been shown to be effective.

Identification

  • It usually grows as a biennial, first forming a rosette and later an erect plant up to 1.6 m tall.
  • Leaves are deeply lobed and spiny, with older leaves showing a prominent white central vein.
  • The upper stems branch profusely and have spiny wings.
  • Purple or pink, rarely white, flower heads droop to one side, giving the plant its common name.
  • Look-alike: Slender thistles (Carduus pycnocephalus and Carduus tenuiflorus) and spear thistle (Cirsium vulgare) have purple or pink flowers and greenish leaves, but nodding thistle is most readily distinguished by its drooping flower heads.

Where it grows

In Australia it occurs in temperate pasture, grassland and roadside habitats, commonly on the Northern, Central and Southern Tablelands of New South Wales and sporadically in south-eastern Queensland, Victoria and Tasmania.

Why it matters

  • Dense patches displace desirable pasture species and reduce carrying capacity.
  • Stock generally avoid the spiny foliage, and the thistle can discourage grazing of neighbouring pasture plants and impede stock movement.
  • Thistle exudates restrict the growth of nearby pasture.
  • In native grasslands it can invade disturbed areas and persist if unchecked.

How it spreads

  • It reproduces only by seed, and a single plant can produce up to 120,000 seeds.
  • Most seed falls within 2 m of the plant; wind is not a major dispersal route, and seed is usually not blown more than 10 m.
  • Longer-distance spread occurs through human activity, including on machinery, in soil, on livestock, in hay and as a contaminant of agricultural seed; seed may also be carried in water.

Control options

  • Maintain healthy perennial pasture with good ground cover through summer and into autumn to reduce seedling establishment.
  • Use registered herbicides at suitable growth stages; seedlings and small rosettes are preferred targets, and spring treatment when the first buds are obvious has been effective.
  • Hand-remove isolated plants or grub small populations, digging plants out to at least 5 cm deep.
  • Goat grazing can reduce seed set by targeting flower heads; slashing in bud or early flowering needs follow-up to kill regrowth, and heads from plants in full flower should be collected and burnt.

Hygiene and washdown

  • Seed can be moved on machinery, in soil, on livestock, in hay and as a contaminant of agricultural seed, so avoid moving these materials from infested sites.
  • 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 3 of 11 regions. Regional priority weed in Greater Sydney, Hunter, Northern Tablelands. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: State prohibited weed. State prohibited weeds are the highest priority: the Victorian Government is responsible for eradicating them, so report any sighting to Agriculture Victoria.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Declared pest (C1), prohibited. C1 Exclusion: to be kept out of WA, or out of the parts of WA where it is not established. Report any sighting to DPIRD. It must not be brought into WA (prohibited organism).
  • 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: 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
  • Tasmania: Biosecurity Act 2019 (Tas), administered by Biosecurity Tasmania

Sources