Biosecurity Spotters logo

Spear thistle (Cirsium vulgare)

Spear thistle is a highly competitive weed of fertile farmland in temperate Australia and can cause serious production losses. Its spiny plants compete with pasture, deter stock from grazing and can contaminate wool and hay.

Key facts

Type: Weed, herb.

Native to: Europe, western Asia and northern Africa.

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

Other names: Black Thistle, Scotch Thistle.

Best time to act: Look for seedlings after autumn rain and again in late winter or early spring, and treat before the central flowering stem develops when practicable.

Identification

  • It is an erect annual or biennial herb, usually 600 mm to 1.5 m tall, that starts as a basal rosette of spiny leaves.
  • The leaves are toothed or lobed, with spiny margins; stem leaves extend down the stem to form deeply lobed, spiny wings.
  • Purple to pink, rarely white, flowers grow in large heads at the ends of stems and branches, usually in summer and autumn.
  • The flower heads have several rows of spiny green bracts, and the grey to light-brown or almost black seeds have a pappus of soft feathery hairs.
  • Look-alike: Perennial thistle (Cirsium arvense) has rhizomatous roots and smaller flower heads, and does not have wings along its stems.
  • Look-alike: Nodding thistle (Carduus nutans) has drooping flower heads and purplish bracts, unlike spear thistle’s erect heads and green, spine-tipped bracts.

Where it grows

In Australia it occurs in temperate and subtropical areas, especially fertile, open sites such as pastures, cropland, roadsides and disturbed areas, and is limited to uplands in tropical north-eastern Australia.

Why it matters

  • It competes with desirable pasture plants for moisture and nutrients and can reduce carrying capacity and production.
  • Its spines deter stock from grazing, contaminate wool and hay, and may make shearing difficult or transmit virus diseases between animals.
  • It can invade disturbed native grasslands, open woodlands and conservation areas, and is also a weed of gardens, urban parks and roadsides.

How it spreads

  • Seeds spread short distances by wind; most fall within 2 m of the parent plant, although seeds with their pappus intact have been measured travelling more than 30 m.
  • Most seed is spread by machinery, vehicles, flowing water, livestock, contaminated seed and fodder.

Control options

  • Use registered herbicides, with seedlings generally most susceptible; where practicable, treat before the central flowering stem develops.
  • Cultivate infested areas while plants are rosettes, then follow up new seedlings and regrowth.
  • Maintain healthy perennial pasture throughout the year, especially through summer into autumn, and re-sow perennial pasture where needed to reduce reinfestation.
  • Goats will eat flowers, seed heads and stems at the flowering stage, which can reduce seed production over several seasons.

Hygiene and washdown

  • Seeds can be carried in soil attached to machinery and vehicles, and in contaminated seed, fodder and agricultural produce; 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: 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: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Permitted, not declared. Listed as a permitted organism in WA, so it can be brought in, but it is not a declared pest.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • 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
  • Tasmania: Biosecurity Act 2019 (Tas), administered by Biosecurity Tasmania
  • 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