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Taurian thistle (Onopordum tauricum)

Taurian thistle is a sleeper weed recorded at only three localities in Victoria, although it has persisted locally at two of them. It could become a serious agricultural weed and may also affect disturbed native vegetation and urban areas.

Key facts

Type: Weed, herb.

Native to: Western Asia and eastern and south-eastern Europe.

Established in: VIC.

Other names: Scotch Thistle.

Best time to act: Look for rosettes after germination and flowering plants in the second spring–summer; spring is the best time for a single herbicide application.

Identification

  • A biennial herb that first forms a basal rosette, then develops erect, spiny, winged stems up to 2 metres tall.
  • Leaves are green, oblong-lanceolate and divided into 6–8 pairs of triangular lobes tipped with yellow spines; the upper surface is sparsely glandular-hairy and the lower surface is more densely hairy or cobwebbed.
  • The ribbed, winged stems have sparse glandular and multicellular hairs; the wings are up to 15 mm wide and have spines up to 5 mm long.
  • Purplish-pink flower-heads are 55–70 mm across, solitary or clustered near branch ends; the brown, wrinkled fruits are 5–6 mm long and have a cream-coloured pappus.
  • Look-alike: Scotch thistle (Onopordum acanthium) and Illyrian thistle (O. illyricum) have similar growth habits but whitish, woolly-hairy stems and leaves, unlike the green, sparsely glandular-hairy leaves and green to brownish stems of Taurian thistle.
  • Look-alike: Nodding thistle (Carduus nutans) has more deeply divided, more spiny leaves; its flower-head receptacle is not pitted, unlike the deeply pitted receptacle of Onopordum species.

Where it grows

In south-eastern Australia it occurs in pasture and rangelands, with records in Victoria and a record from near Orroroo in South Australia; it establishes in open, disturbed or degraded areas.

Why it matters

  • It can occupy pasture, deter grazing animals and people, contaminate fodder and grain, and invade grain crops, reducing growth and contaminating marketable grain.
  • Severe infestations can form tall, dense, impenetrable stands that restrict access to foraging and watering areas and may harbour pest species.
  • It may reduce pasture carrying capacity by more than 5% and could contaminate wool.
  • In grasslands and open scrub it can compete with native plants, reduce food available to native animals and add dried vegetation to the fuel load, potentially increasing fire intensity.

How it spreads

  • It reproduces entirely by seed, with each flower-head producing up to several hundred seeds.
  • The seed has a terminal pappus and may be dispersed a short way by wind; in other Onopordum species, seeds may fall near the parent plant when the pappus comes away.
  • Wider dispersal is likely via contaminated fodder, livestock, machinery and vehicles.

Control options

  • Use registered herbicides as part of an overall management program; if making a single herbicide application, spring is identified as the best time, and herbicides are most effective on seedlings and young rosettes.
  • Hand-chipping is effective for low-density plants; remove as much of the taproot as possible, and uproot seedlings or young rosettes during cultivation.
  • Maintain dense, vigorous pasture and good ground cover to reduce seedling establishment; reducing stock levels can allow perennial grasses to establish.
  • Goats can eat thistles at rosette, flowering and post-flowering stages, reducing seed production; mowing or slashing before flowering may prevent seed set temporarily, but plants can regrow.

Hygiene and washdown

  • Contaminated fodder, livestock, machinery and vehicles are identified as likely wider dispersal pathways; take care not to move seed-bearing material between 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: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • 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.

  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria

Sources