Mexican Poppy

Argemone ochroleuca

Quick facts

Status

Permitted

Life Cycle

Annual

Growth Form

Herb

Origin

Mexico & central America

Flowers

Yellow

Dispersal

Vehicles, water and hay

Toxicity

Toxic to humans and animals

Names

Other Common Names: Mexican prickle poppy, Mexican thistle, devil's fig, golden thistle of Peru, prickly poppy, white thistle, yellow poppy

Synonyms: Argemone mexicana.

Form and function

Grows to 1.5 m tall and can reach maturity in approximately 2 to 3 months. Seeds may remain viable in the soil for up to seven years, contributing to long-term persistence and reinfestation.

Flowers

•    Flowers can grow up 7 cm in diameter.
•    Four to six petals on each flower.
•    Individual petals are about can grow up to 4 cm long.
•    Flowers occur individually at the ends of branches.
•    Each flower has three sepals that are spiny.
•    Sepals can grow up to 20 mm long and have a terminal spine about 8 mm long.
•    Numerous bright yellow stamens and a purple stigma are present in the centre.

Leaves

Bluish/green to greyish/green.
Often have whitish veins and markings.
Up to 20 cm long and up to 6 cm wide.
Leaf margins have many small yellowish spines (about 5 mm long).
Basal leaves form a rosette but wither as the plant matures.
Stem leaves are arranged alternately along the stem.

Fruits

Oblong/oval shaped capsule.
Up to 5 cm long and up to 2 cm wide.
Capsules are covered in rigid spines.
Open at the top when mature.
Each capsule may contain up to about 400 seeds.
Seeds are up to 2 mm in diameter and brown/black in colour.

Roots

A stout taproot is present.

Habitat

Establish its habitat mainly in temperate and tropical environment, and from arid to humid with variety of soil types. It can grow in wide range of highly disturbed environments and large infestations can be observed along seasonal sandy riverbeds, roadsides and mining areas.

May be confused with...

Similar non-native species: Similar to Mexican prickly poppy (Argemone mexicana) however it can be distinguished by its flowers as Argemone mexicana has bright yellow flowers while Argemone ochroleuca has creamy yellow flowers. Argemone mexicana is a C1 declared plant and needs to be reported.

How does it spread?

Seeds are dispersed through livestock movement, vehicle traffic, waterways, hay, and grain. Each plant can produce around 30,000 seeds, contributing to its rapid spread.

Why is it a weed?

Extremely poisonous to both human and animals. However, due to its unpalatable tastes, poisoning incident is rare. Currently, dense infestations are observed in Pilbara region along water courses.

History

First recorded in 1882 in New South Wales as a contaminant in imported wheat. In 1921, Mexican poppy was recorded first time in Western Australia in Beverley in the Avon Valley catchment.

How to control

Physical

Chemical

Physical

Preventing seed production is critical for effective Mexican poppy control due to its prolific seed production. Hand-pulling is suitable for isolated plants and small infestations but is generally impractical for larger infestations because of the labour required. Care should be taken to prevent seed spread when removing mature plants. As seeds can remain viable in the soil for up to seven years, follow-up monitoring and control are essential.

For small infestations, removing flowers before they set seed can help reduce future infestations and gradually deplete the seedbank.

PPE: Wear gloves when handling plants, as the spines are sharp and the sap is poisonous.

Chemical

For small infestations, spot spray with glyphosate (360g/L) at 1-2% w/v or use the following broadleaf selective herbicides

2,4-D (625 g/L): Mix 50 mL per 15L water.
MCPA (340 g/L) + dicamba (80 g/L): Mix 50 mL per 15L water.

Spray evenly across the foliage until leaves are thoroughly wet. Seedlings are generally easier to control than mature plants.

For large infestations, apply a foliar spray with glyphosate (360g/L) at 1-2% w/v before flowering or use the following broad leaf selective herbicides:

2,4-D (625 g/L): Mix 320 mL per 100 L water.
MCPA (340 g/L) + dicamba (80 g/L): Mix 350 mL per 100 L water.

Spray evenly across the foliage until leaves are thoroughly wet. Seedlings are generally easier to control than mature plants.