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Three-cornered garlic (Allium triquetrum)

Three-cornered Garlic can form dense stands that dominate the ground layer in bushland, riparian areas, roadsides and gardens. It can taint milk and meat when eaten by grazing animals, and control is difficult because many bulbs and bulblets may remain in the soil.

Key facts

Type: Weed, herb.

Native to: Southern Europe and North Africa.

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

Other names: Angled Onion, Three-Cornered Leek, Triquetrous Garlic, Triquetrous Leek.

Identification

  • A bulbous perennial herb, usually 100–500 mm high, with erect stems that are triangular in cross-section.
  • Its bright green, mostly basal leaves are 150–500 mm long and 5–20 mm wide, and smell strongly of onion when crushed.
  • Drooping, bell-shaped white flowers with green stripes are clustered at the ends of stems.
  • Small white bulbs, 10–20 mm across, have numerous smaller bulblets attached.
  • The green, ovoid capsule is 4–6 mm in diameter and 6–7 mm long, and contains black oblong seeds.
  • Look-alike: Snowdrop (Leucojum vernum) is similar, but has no green spots on its leaves and no odour.

Where it grows

In Australia it occurs in ACT, NSW, SA, TAS, VIC and WA, with older records indicating it was formerly naturalised in Queensland, and favours moist or poorly drained soils such as creek lines, roadsides, urban areas, pastures and bushland.

Why it matters

  • In suitable conditions, dense stands can dominate the ground layer and crowd out native grasses and ground covers.
  • It can impede regeneration of over-storey vegetation and leave soil bare during its summer dormancy.
  • It does not compete strongly with crops and improved pastures, but can taint dairy products and meat with an onion flavour and unpleasant odour, making them unfit for sale.
  • It can dominate riparian, roadside, bushland and domestic garden areas.

How it spreads

  • Bulbs and seeds can spread in agricultural produce and in mud sticking to animals, machinery and vehicles.
  • It also spreads in garden refuse and contaminated soil moved during road grading or used as garden top dressing.

Control options

  • Control is difficult because many bulbs and bulblets can be present in the soil, and follow-up over several years is usually required.
  • For small numbers of outliers, physically remove the plants and all bulbs; this is not effective for larger populations.
  • Autumn and spring cultivation can kill plants, but needs to be repeated for several years; it can be combined with spraying just before flowering.
  • In bushland, spot spray with registered herbicides just before flowering, following the relevant product directions and approved methods.

Hygiene and washdown

  • Mud on animals, machinery and vehicles can carry bulbs and seeds, so take care not to transport mud from infested areas.
  • Avoid moving contaminated soil or garden refuse, which can spread the plant.
  • 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: Restricted weed. 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: 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.

  • 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
  • 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