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Johnson grass (Sorghum halepense)

Johnson grass is widespread in Australia and can cause serious crop losses through competition and chemical inhibition of other plants. It can also host crop pests and diseases, and may poison livestock under certain conditions.

Key facts

Type: Weed, grass.

Native to: The narrow-leaved Australian ecotype originates in the Mediterranean; a more robust tropical type ranges from southern India to western Pakistan..

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

Other names: Aleppo Grass, Barool, Baru Grass, Egyptian Millet.

Best time to act: Look for seedlings in spring and early summer, and treat early in the season, with spraying recommended during the first two weeks of seasonal growth.

Identification

  • A perennial, tussock-forming grass that grows to about 2 m high.
  • Upright stems arise from creeping, branched, scaly underground stems that are often purple-spotted.
  • Leaves are mostly hairless, flat and 20–50 cm long, with rough edges and a prominent midrib.
  • The pale green to purplish seed-head is 10–35 cm long, with loosely spreading branches.
  • Seeds are reddish brown to black, egg-shaped and about 3–4 mm long.
  • Look-alike: It can be confused with Columbus grass (Sorghum × almum). Johnson grass has more long-pointed flower clusters, and its seeds are slightly smaller, but these differences can be hard to see, especially in mixed samples.

Where it grows

In Australia it occurs in tropical to temperate wetter areas, especially along roadsides and creek edges, and in crops, pastures and irrigation districts.

Why it matters

  • It competes with crops, inhibits the growth of other plants and can host crop pests and diseases, causing severe crop losses.
  • It may contaminate pollen in nearby cultivated sorghum and hosts the Sorghum Midge and sugarcane mosaic virus.
  • It can poison livestock when plants contain cyanogenetic glycosides, particularly during rapid growth or under some adverse conditions; cattle are more susceptible than sheep.
  • It can invade native vegetation, particularly wetlands, and may restrict visibility on road curves and corners.

How it spreads

  • It spreads mainly by seed, which can be carried by wind, water runoff, animals and birds.
  • Seeds can be moved in agricultural produce and in mud on machinery and vehicles; one plant may produce 80,000 or more seeds in a growing season.
  • It also spreads from rhizomes and shoots, which can break off, take root elsewhere and form new plants.

Control options

  • Use an integrated approach combining crop rotation, cultivation, competing crops and registered herbicides; a single herbicide application is generally not enough for large infestations.
  • Systemic herbicides can reach underground stems; follow up with spot spraying and seedling control, and avoid soil disturbance.
  • Repeated close mowing or heavy grazing can reduce growth and underground stem reserves; follow grazing with herbicide or winter ploughing where appropriate.
  • For suitable sites, consistent tillage or flooding for 3–6 weeks in early spring before underground stems sprout may help; spring burning alone is not recommended because it can promote sprouting.

Hygiene and washdown

  • Clean mud from machinery and vehicles before moving between sites, as it can carry seed.
  • Check agricultural produce and equipment for seed or plant material before transport.
  • 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 Central West. 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: 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)
  • 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
  • Northern Territory: Territory Parks and Wildlife Conservation Act 1976 (NT), administered by NT Department of Lands, Planning and Environment

Sources