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Prickly poppy (Argemone mexicana)

Mexican poppy is an introduced weed recorded in Western Australia, south-eastern Queensland and north-eastern New South Wales, and is most common in Queensland. It can establish on disturbed ground and overgrazed pastures, and its prickly fruits can reduce wool value when they become entangled in it.

Key facts

Type: Weed, herb.

Native to: North America, including Florida and Mexico, and throughout South America.

Established in: QLD, NSW, WA.

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

Identification

  • An erect annual herb that grows up to 1.5 m tall.
  • Its bluish-green or greyish-green leaves usually have whitish veins and small yellowish spines along their edges.
  • The bright yellow flowers are 3–7 cm across, with six petals and numerous yellow stamens.
  • Its spiny, oblong capsules are 2.6–3.6 cm long and contain numerous small seeds.
  • Look-alike: Argemone ochroleuca is very similar, but has cream or pale-yellow flowers and egg-shaped buds, rather than the bright yellow flowers and globular buds of Mexican poppy.
  • Look-alike: American poppy (Argemone subfusiformis subsp. subfusiformis) is known to be naturalised only in north-eastern New South Wales and has generally larger flowers and a less spiny capsule.

Where it grows

In Australia it occurs in Western Australia, south-eastern Queensland and north-eastern New South Wales, in habitats including roadsides, railway lines, waste areas, disturbed sites, degraded pastures, crops, fallow ground, sandy river flats and ephemeral watercourses.

Why it matters

  • It establishes readily on wasteland and overgrazed pastures, but is generally not regarded as an aggressive crop weed in Australia.
  • Its prickly fruits can become entangled in wool and considerably reduce its value.
  • Alkaloids occur in all parts of the plant, and it is suspected of being toxic to animals and humans; reported livestock poisonings are rare because it is unpalatable.
  • It is a host for Verticillium wilt fungus and Tomato spotted wilt virus.

How it spreads

  • It reproduces by seed, and a single plant can produce up to 30,000 seeds per year.
  • Seeds usually fall close to the parent plant but can be dispersed by moving water, particularly in riparian habitats and where erosion and runoff occur.
  • Contaminated soil, fodder and vehicles, as well as the fur and hooves of livestock, can transport seed.

Control options

  • Aim to prevent seed formation.
  • Hand-pull, grub or cut plants before their fruits ripen.
  • Control seedlings with registered herbicides or mowing.
  • Maintain good pasture, as seedlings do not compete well with perennial crop and pasture species or established pasture.

Hygiene and washdown

  • Avoid moving contaminated soil or fodder, and check vehicles for Mexican poppy seed because both are listed as seed-transport vectors.
  • Prevent seed being carried by moving water where plants occur in riparian habitats.
  • 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)
  • 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

Sources