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Black locust (Robinia pseudoacacia)

Black locust can spread by root suckers to form dense thickets that exclude native and other vegetation. It can invade paddocks and is poisonous to stock and people.

Key facts

Type: Weed, tree.

Native to: United States of America.

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

Other names: False acacia, Locust tree, Yellow locust, Robinia.

Identification

  • A fast-growing, deciduous tree usually 10 to 15 metres tall, with paired stout spines on stems and branches.
  • Leaves are divided into 5 to 10 pairs of oval leaflets, with 11 to 21 leaflets in total.
  • White, pink or purplish pea-shaped flowers grow in hanging clusters in spring.
  • It produces hanging, flat, brown woody pods containing 4 to 10 mottled blackish seeds.
  • Look-alike: Honey locust (Gleditsia triacanthos) usually has more than 25 leaflets per leaf, with obscurely toothed edges; its spines are not paired at the leaf bases and its flowers are tiny and yellowish, not pea-shaped.
  • Look-alike: Golden locust is also naturalised to some extent in Queensland, New South Wales and Victoria.

Where it grows

In Australia it occurs in scattered localities from south-eastern Queensland to Adelaide, between Perth and Albany, and near Launceston and Hobart, in places including river flats, grasslands, grassy woodlands, roadsides and abandoned gardens.

Why it matters

  • Root suckers can form dense thickets or copses that exclude native and other vegetation.
  • Suckering plants can invade open paddocks and reduce carrying capacity.
  • All parts of the plant are poisonous to stock, including horses.
  • All parts are poisonous to people and can cause dizziness, nausea, vomiting, diarrhoea, convulsions and drowsiness.

How it spreads

  • It reproduces by seed and root suckers, with root suckers generally more important than seedlings.
  • Disturbing roots or foliage can trigger suckering and the development of dense clumps.
  • Seeds are reported to disperse mostly by gravity and wind; water or movement of soil containing seeds may assist long-distance dispersal.

Control options

  • Young seedlings with a taproot can be physically removed.
  • Avoid disturbing roots or cutting down established trees without a follow-up plan, as this can trigger dense suckering.
  • Use registered herbicides with suitable woody-weed methods such as cut-stump or drill-and-fill treatment.
  • Follow-up control is required, and removal of suckers may need to be ongoing.

Hygiene and washdown

  • Avoid moving soil that may contain seeds, as movement of soil containing seeds may assist their long-distance dispersal.
  • 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 North Coast. 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: 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: Declared pest, prohibited. It is a declared pest throughout the ACT. Dealing with it, such as selling, moving or keeping it, is prohibited.

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