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Sourgrass (Digitaria insularis)

Sourgrass is an introduced perennial grass that can become a persistent weed in warm parts of Australia. Its dense growth can compete with crops and pasture, and established plants are difficult to control if they regrow or set seed.

Key facts

Type: Weed, grass.

Native to: Tropical and subtropical America.

Established in: QLD.

Other names: Brazilian crabgrass, woolly fingergrass.

Best time to act: Look for it when its conspicuous flower heads are present, and treat actively growing plants before they set seed.

Identification

  • It grows as an upright, perennial tussock, with long, narrow leaves.
  • The leaves and stems can be rough or hairy.
  • Flower heads form loose, spreading clusters above the leaves.
  • The flower clusters have a distinctive soft, fluffy look from the long silky hairs around the spikelets.
  • Look-alike: Other tall grasses, including native fingergrasses, may look similar; the fluffy, long-haired flower clusters are a useful feature to check.

Where it grows

In warm Australian regions it can grow in open, disturbed places such as roadsides, pastures and cropping areas.

Why it matters

  • Dense tussocks compete with crops and pasture plants for space, light and resources.
  • Its perennial growth makes infestations persistent and regrowth can make control difficult.
  • Plants that set seed can contribute to further spread and increase the effort needed for management.

How it spreads

  • Seeds can be carried by wind and moved in contaminated soil, fodder or machinery.
  • Seeds may also be transported on vehicles, boots and other equipment.
  • Plant crowns or root material moved with soil can help spread infestations locally.

Control options

  • For small infestations, dig out plants carefully, removing the crown and as much root material as possible, and prevent plants from setting seed.
  • For larger infestations, use only herbicides registered for the site and target plant, and follow the product label and local advice.
  • Inspect treated areas regularly and follow up regrowth and new seedlings before they flower or set seed.
  • Where relevant, report suspected new infestations to the state or territory biosecurity agency.

Hygiene and washdown

  • Clean soil and plant material from machinery, vehicles, boots and tools before leaving an infested site.
  • Avoid moving contaminated soil or fodder, especially when seed heads are present.
  • 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: Declared pest (C1), prohibited. C1 Exclusion: to be kept out of WA, or out of the parts of WA where it is not established. Report any sighting to DPIRD. It must not be brought into WA (prohibited organism).
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Declared weed. Weeds Australia lists it as a declared weed in the NT under the Weeds Management Act 2001. Check the NT declared weeds list for its class and what it requires.
  • 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)

Sources