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Mexican poppy (Argemone ochroleuca)

Mexican poppy can form dense populations that impede the movement of stock and wildlife and displace native vegetation. It is poisonous to humans and animals, and can affect some crops and reduce wool value when prickly fruits become tangled in it.

Key facts

Type: Weed, herb.

Native to: Upland, less humid parts of Mexico.

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

Other names: Prickly Poppy, Mexican Thistle, White Thistle, Devil’s Fig.

Best time to act: Look for winter rosettes and flowering stems in spring; treat before fruits ripen, with flowering most common in spring and summer.

Identification

  • An erect, prickly annual herb that usually grows to 1 m tall but can reach 1.5 m, with a stout tap-root.
  • Its bluish-green or greyish-green leaves have whitish veins or markings, are deeply divided into lobes, and have yellowish spines along their edges.
  • Damaged stems exude yellow sap.
  • Flowers are 3–7 cm across, with pale yellow to cream petals; the spiny capsules are 2–5 cm long and contain numerous small seeds.
  • Look-alike: Argemone mexicana has bright yellow flowers and globular flower buds, unlike the pale yellow to cream flowers and oval buds of Mexican poppy.
  • Look-alike: American poppy (Argemone subfusiformis subsp. subfusiformis) has generally larger flowers and a less spiny capsule.

Where it grows

In Australia it occurs across a wide range of climates and habitats, including roadsides, railway lines, disturbed sites, degraded pastures, crops, fallow ground, sandy river flats and ephemeral watercourses.

Why it matters

  • Dense populations can impede the movement of stock and wildlife and displace native vegetation.
  • It is poisonous to humans and stock, although stock rarely eat it; poisoning can occur through contaminated feed, hay or chaff.
  • Prickly fruits can become entangled in wool and reduce its value.
  • It grows in sugarcane and cereal crops and can affect crops such as sugarcane, cereals and vegetables.

How it spreads

  • A single plant can produce up to 30,000 seeds per year, which usually fall close to the parent plant.
  • Moving water disperses seed, particularly in riparian habitats and where erosion and runoff occur.
  • Seed can also be transported in contaminated soil, fodder and agricultural produce, on vehicles, and on the fur and hooves of livestock.

Control options

  • Aim to prevent seed formation.
  • Hand-pull, grub or cut plants before any fruits ripen.
  • Good pasture management helps reduce impacts and prevent invasion because seedlings compete poorly with established pasture and perennial species.
  • Slashing or mowing reduces seed production; seedlings can also be controlled with registered herbicides.

Hygiene and washdown

  • Avoid moving contaminated soil, fodder or agricultural produce, which can carry seed.
  • Check vehicles and machinery for seed-bearing material before moving between sites, as they can transport seed.
  • 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: 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
  • Australian Capital Territory: Biosecurity Act 2023 (ACT), administered by ACT Biosecurity
  • 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