Mexican poppy

Mexican poppy is a declared Class B and Class C weed.

Another name for this plant is Argemone ochroleuca.

Mexican poppy - infestation 

Identification

You should use this as a guide. There may be other plants or weeds that look similar.

If you are unsure, contact the Weed Management Branch.

Habit

These features describe the habit of this plant:

  • robust, erect annual herb
  • up to 1m tall
  • found in seasonal creeks, streambeds, drainage lines and disturbed areas.

Mexican poppy - habit and spread 

Stems and branches

These features can identify the stems and branches:

  • release a yellow sap when cut
  • smooth branches covered with stiff yellow prickles.

Mexican poppy - stems and branches 

Leaves

These features can identify the leaves:

  • distinctive pale blue-green
  • all parts are toxic to humans and animals
  • leaves folded into multiple points ending in stiff yellow prickles.

Mexican poppy - leaves 

Flowers

These features can identify the flowers:

  • single flowers at the end of branchlets
  • four to six cream-pale yellow petals
  • about 6cm across.

Mexican poppy - flowers 

Fruit and seeds

These features can identify the fruit and seeds:

  • fruit are shiny bluegreen capsules
  • covered in rigid spines
  • opening at the top to expose seeds
  • each capsule contains up to 400 seeds
  • seeds are brown or black
  • 1.5mm in diameter.

Mexican poppy - fruit and seeds 

Impact

Mexican poppy can have all of the following impacts:

  • all parts of the plant are toxic to humans and animals but it is generally avoided
  • can compete with crops and pastures
  • can contaminate feed and poison poultry and other livestock
  • rapidly invades disturbed country
  • proliferates in dry river beds affecting amenity
  • impacts tourism, camping and recreational use of creeks and rivers.

Habitat and distribution

Mexican poppy is native to Mexico, but also occurs naturally in Texas and Central America. It was introduced to Australia accidentally in the early 1800s possibly as a contaminant in wheat seed.

It generally establishes on disturbed ground, spreading along roadsides, riverbanks, sandy flats and the beds of intermittent streams. 

It was first recorded in Australia in 1845. It has since become troublesome in Queensland, New South Wales, and Western Australia.

In the NT Mexican poppy is now well established throughout multiple central Australian river systems and there are scattered infestations on the road and rail corridors.

It prefers subtropical and semi-arid climates where it can grow on a wide range of soil types, especially those that keep high moisture during summer.

Spread prevention

Mexican poppy is only propagated by seed, which tend to fall near the parent plant, sometimes leading to dense, almost pure stands, but they can be spread by water.

Accidental spread is a problem, through the transfer of contaminated construction materials Inadvertent transport of seed has occurred from river sand extracted from the numerous sand mining extraction licences established in the Todd River and Roe Creek as well as the points of sale of river sand used primarily for construction and back filling.

Users of construction and landscaping products should be aware of the potential for weed spread and establishment. 

In central Australia new infestations of Mexican Poppy have recently developed in areas where river sand and gravel have been used for landscaping and construction purposes.

You can prevent the spread of Mexican poppy by doing all of the following:

  • ask your supplier if the products to be provided are weed free
  • avoid suppliers who have previously provided contaminated product
  • cover or limit your load to avoid spillage during transport
  • keep material contained and make sure no material stays on site
  • map infestations to help develop a management plan
  • report and manage any new outbreaks immediately
  • designate wash down areas and actively work to prevent contamination of clean areas
  • monitor all areas which have had river sand or gravel introduced
  • monitor areas that you have treated and watch for re-infestations.

Control

Chemical control

The best time to treat Mexican poppy is from December to February. Below is a list of chemicals and treatment methods that can be used.

Chemical and concentration Rate Situation, method and notes
2, 4-D amine 625 g/L
Various trade names
320ml / 100 L Seedling or adult (individuals or infestation):
Foliar spray - apply when actively growing
Glyphosate 360 g/L
Various trade names and formulations
10ml /1 L Seedling or adult (individuals or infestation):
Foliar spray - apply when actively growing
MCPA 340 g/L + Dicamba 80 g/L
Various trade names
350ml / 10 0L Seedling or adult (individuals or infestation):
Foliar spray

Non-chemical control

Non-chemical control aims to limit the production and spreading of seeds. Seeds stay dormant in the soil for up to seven years, so getting rid of the weed needs regular follow up control for several years.

Hand pulling and grubbing

Weeds, including their roots, are physically pulled out of the ground by hand or using hand tools. This is an effective method of control for individual weeds and recent outbreaks that haven’t released seeds yet, but it requires a lot of labour.

Take extra precautions to stop seed spread if removal is required once the plants are already seeding.

Last updated: 27 June 2017