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Cayenne snakeweed (Stachytarpheta spp.)

Cayenne snakeweed was introduced to Australia as an ornamental plant and can invade pastures and crops, including sugarcane. It can also outcompete native plants, so land managers should identify and control plants and watch for regrowth.

Key facts

Type: Weed, shrub.

Native to: Tropical Americas, from the Caribbean to Argentina.

Established in: QLD, NSW, WA, NT.

Best time to act: Look for plants throughout the year, especially when they flower in summer and autumn, and spray actively growing plants in summer for best results.

Identification

  • It is an evergreen, clumping perennial shrub, usually up to 1.5 m tall but sometimes reaching 2.5 m.
  • Its leaves are opposite, oval, 2–10 cm long and 1–5 cm wide, with toothed edges, pointed tips and prominent veins.
  • Blue, purplish or sometimes white tubular flowers with five spreading petals grow along curved spikes 10–45 cm long.
  • Flowers are present throughout the year, mostly in summer and autumn; as they dry and fall, the spike develops a snakeskin-like appearance.
  • Stems are slender and branched, greenish or purple-tinged and four-angled when young, becoming light brown, woody and round when mature.

Where it grows

In Australia it grows in tropical and subtropical climates, especially wet coastal areas, along waterways and forest edges, and in pastures, rangelands and sugarcane crops.

Why it matters

  • It can rapidly invade pastures and reduce productivity.
  • It can invade crops, including sugarcane.
  • It can outcompete and suppress native plants.
  • It spreads quickly where ground cover is reduced.

How it spreads

  • Seeds germinate throughout the year when soil moisture is sufficient.
  • Seeds can be carried on machinery, vehicles, animals and clothing, and moved in contaminated hay, pasture seed or soil.
  • People can spread it by dumping garden waste.

Control options

  • For individual plants, pull or dig them out and remove the larger roots.
  • Large infestations can be slashed before flowering, but slashing does not kill the plants and follow-up treatment is needed.
  • For heavy infestations, destock the paddock, treat the plants and re-establish dense pasture; use a herbicide registered for the site and follow its label and any permit conditions.
  • Check treated areas for regrowth and new seedlings, and contact the local council weeds officer for identification advice.

Hygiene and washdown

  • Clean soil and plant material from machinery, vehicles, footwear and other equipment before moving between sites.
  • Avoid moving contaminated soil, hay or pasture seed, and do not dump garden waste.
  • 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: Not listed. Not found in the Western Australian Organism List. Check with DPIRD before moving or keeping it.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Declared weed, Class B. Class B: growth and spread must be controlled. All declared weeds are also Class C, so they must not be brought into the NT.
  • 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
  • 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