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Tumbleweed (Amaranthus albus)

Tumbleweed is a serious weed of agriculture and disturbed areas in southern Australia, where it can form dense stands and invade some open or degraded native vegetation. Each plant can produce tens of thousands of seeds, and plants that break off at the base can roll in the wind and spread seed over long distances.

Key facts

Type: Weed, herb.

Native to: Southern North America.

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

Other names: Stiff Tumbleweed, White Pigweed, Tumble-weed.

Best time to act: Look for it during summer growth, with flowering and fruiting from mid-summer to early autumn, sometimes as early as December and as late as May.

Identification

  • This summer-growing annual herb is low-growing and erect to spreading, reaching about 80 cm tall and sometimes more than a metre wide.
  • Its rigid, branching stems are usually whitish and hairless, though plants may sometimes be tinged red or purple.
  • Leaves are alternate, usually 5–20 mm long and 2–10 mm wide, with pale veins and smooth, untoothed margins.
  • Small clusters of 2–5 flowers grow between the leaves and stems, surrounded by spiny bracts.
  • The small, wrinkled or blistered fruits are capsules that usually split around the middle; they contain shiny brown to black seeds about 1 mm across.
  • Look-alike: Fat Hen (Chenopodium album) has toothed leaves and flowers without spiny bracts; Tumbleweed has smooth leaf margins and spiny bracts around its flowers.
  • Look-alike: Prickly Saltwort or Roly-poly (Salsola australis) has narrower, often succulent leaves and winged fruits; Tumbleweed has fruits that usually split evenly around the middle.

Where it grows

In Australia it occurs in urban and modified landscapes, cultivated and wasteland areas, stream banks, roadsides and railway lines, and on edges of native vegetation, across temperate to semiarid areas and some subtropical areas.

Why it matters

  • It is a serious weed of agriculture and crops and can form dense stands.
  • A plant can produce tens of thousands of seeds, which may persist in the soil seed bank over several crop rotations.
  • It can invade open or degraded native vegetation, especially where surrounding agricultural or modified areas are heavily infested.
  • In North America it hosts crop-damaging fungal and viral diseases, nematodes and insects; this has not been documented in Australia but may pose a problem in badly infested crops.

How it spreads

  • When mature, the fruit capsules split around the middle and release seeds to the ground.
  • Mature plants may break off at the base and roll in the wind across open ground, distributing seeds.
  • Seeds can also spread in contaminated soil and gravel during earthworks, and in wet soil carried on machinery, vehicles and people.

Control options

  • Small infestations and individual plants may be removed by hand pulling or digging them out.
  • Mechanical control is used especially in agriculture; mowing or tillage has been suggested as useful methods in the United States.
  • Amaranthus species may be susceptible to selective and non-selective herbicides, but resistant biotypes have been reported; consult the APVMA for current registered herbicides.

Hygiene and washdown

  • Avoid moving contaminated soil or gravel from infested sites, as seeds can be spread during earthworks.
  • Check and clean machinery, vehicles and footwear or gear carrying wet soil before moving from an infested site.
  • 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: Permitted, not declared. Listed as a permitted organism in WA, so it can be brought in, but it is not a declared pest.
  • 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.

  • 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