Silybum marianum

Variegated thistle

Also known as:

Milk thistle

Family: Asteraceae

Origin: Europe, Mediterranean

Close up of centre of Variegated Thistle plant.
A large prickly thistle that can grow up to 2.5m tall. Leaves are striking with green and white variegations.
Photo credit: Jonathan Boow

Regional Pest Management Plan (RPMP) status

  • Hauraki Gulf Controlled Area Notice pest
  • Whole region — Sustained control

View more about the RPMP statuses

General description

Large annual or biennial prickly thistle < 2.5 m tall and < 2 m in diameter. Leaves are variegated, with white veins and blotches. Flowers are purple, surrounded by spines and borne in late spring – summer. Achenes bear pappus and ripen in summer – autumn.

What you need to know

To help protect our environment:

  • you must not breed, distribute, release or sell variegated thistle within the Auckland region
  • you must not plant variegated thistle within the Auckland region
  • you must destroy any variegated thistle plants on land that you occupy.


Pasture, croplands, river flats, roadsides.


Seeds dispersed by wind and contaminated soil, machinery and animals.

Impact on environment

Competes with valued pasture plants. Can be toxic to livestock.


Site management

Maintaining good pasture cover can prevent establishment or suppress an infestation. Prevent overgrazing especially in summer. Other herbicides are available for selective use in pasture.

Recommended approaches

Physical control

Method: Dig or grub out at least the first 5cm of taproot.

Plant parts requiring disposal: Seeds.

Disposal options: Remove to greenwaste or landfill if practical.


Biocontrol is currently not available for this species.

Community agrichemical control recommendations

No qualifications: Foliar spray with 100ml glyphosate green per 10L of water.

Certified Handler/Experienced agrichemical user: Foliar spray with 100ml glyphosate green per 10L of water and 20ml penetrant.

Safety notes

Plant has spines.

Caution: When using any herbicide or pesticide please read the label thoroughly to ensure that all instructions and safety requirements are followed.

Close up of Variegated Thistle flower.
Flowers are purple and surrounded by spines to prevent grazing. Variegated thistle likes to grow in pasture and can take over farms as livestock do not like to eat the spiky leaves.
A young Variegated Thistle.
Variegated thistle flowers are a favourite of bumble bees and butterflies. Once pollinated many seeds are formed on white fluff that is then carried away by the wind.
Photo credit: Jonathan Boow