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Creeping knapweed (Leuzea repens)

Creeping knapweed is a competitive agricultural weed that can form dense patches and reduce crop and pasture productivity. Its extensive, creeping root system makes it difficult to control and can spread the weed when fragments are moved.

Key facts

Type: Weed, herb.

Native to: Eastern Europe to Asia Minor and Mongolia.

Established in: QLD, NSW, VIC, SA.

Other names: Russian knapweed, Hardheads, Hardhead thistle, Blueweed.

Best time to act: Look for active shoots in spring and summer, and treat small patches promptly, with follow-up to catch regrowth.

Identification

  • An upright or ascending perennial herb, usually growing to 800 mm to 1 m tall.
  • It has slender, ribbed stems that branch freely near the top, with variable leaves that have no spines.
  • Pinkish or purple, thistle-like flower heads grow individually at branch ends; they resemble small spear thistles but have no prickles.
  • The underground system includes creeping stems in the top 300 mm of soil, which can extend up to 2 m, and roots that can grow 5 to 7 m deep.
  • Look-alike: Spear thistle has similar flower heads, but is prickly; creeping knapweed has no prickles.
  • Look-alike: Spotted knapweed has brown or black tips on its flower-head bracts, unlike the green to white bracts of creeping knapweed.

Where it grows

In Australia it occurs in Queensland, New South Wales, Victoria and South Australia, in crops and pastures as well as along roadsides, channel banks and other disturbed sites, particularly in semi-arid to sub-humid temperate areas.

Why it matters

  • Dense patches can smother and exclude other plants, compete for water and nutrients, and reduce crop and pasture productivity.
  • It can reduce dryland cereal yields by as much as 75% or more in affected areas, and dryland cropping yields by as much as 80% in some circumstances.
  • It has little feed value; sheep may graze it, but eating large amounts may be poisonous.
  • Prolonged contact may cause skin sensitisation and dermatitis in people.

How it spreads

  • Its main means of spread is its creeping root system; root fragments as short as 2.5 cm can produce shoots.
  • Cultivation equipment can drag root fragments to new areas, and grazing animals may move plant material after pulling plants from the ground.
  • Seeds usually fall close to the parent plant, but seed heads and seeds can be moved by water, contaminated seed, machinery, animals, sacking, mud or fodder.

Control options

  • Find and treat small patches early with registered herbicides, such as spot spraying, and follow up to control regrowth and new seedlings.
  • Seedlings in new, small infestations can be chipped out, removing the roots.
  • Repeated cultivation may control it in some settings, but can move root fragments and spread the weed; it is best avoided in pasture and broadacre cropping.
  • Competition from lucerne, clover or perennial pastures, together with regular cutting or grazing, can help control it.

Hygiene and washdown

  • Clean farm equipment and other machinery before moving between infested and clean areas, because root fragments can be carried and establish new infestations.
  • Avoid moving contaminated seed, fodder, mud or other material that may carry seeds or plant fragments.
  • 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 1 of 11 regions. Regional priority weed in Murray. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Regionally prohibited / regionally controlled / restricted weed (varies by region). Where it is regionally prohibited, landowners must take all reasonable steps to eradicate it on their land. 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: 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.

  • 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
  • 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

Sources