Californian thistle

General description

Rhizomatous perennial herb. Leaves are sessile, < 15 x 5 cm and oblong, with prickles < 1 cm long. Flowers are red/pink/purple and borne in December – February. Achenes have white pappus attached.

What you need to know

To help protect our environment, from 1 September 2021, you:

• will not be allowed to breed, distribute, release or sell Californian thistle within the Auckland region.
• will not be allowed to plant Californian thistle within the Auckland region, unless you are transferring an existing plant on your land to another location within the boundaries of the same property.
• must destroy any Californian thistle on land that you occupy if it has been planted in breach of the above rules and you are directed to do so by an authorised person.

Habitats

Pasture, roadsides, riparian margins, open coastal areas.

Dispersal

Seeds dispersed by wind. Vegetative spread from rhizomes. Human-mediated dispersal through contamination of machinery.

Impact on environment

Infests pasture, reducing milk and animal yields due to herbivore avoidance. Spines injure livestock’s mouths, promoting ‘scabby mouth disease’. Seed heads contaminate wool.

Control

Site management

Maintaining good pasture cover can prevent establishment or suppress an infestation. Mowing before flowering will reduce spread of seeds.

Recommended approaches

Physical control

Method: Dig or grub out.

Plant parts requiring disposal: Seeds.

Disposal options: Remove to greenwaste or landfill if practical.

Biocontrol

Check for presence of agents:

• Californian thistle gall fly ( Urophora cardui).
• Californian thistle leaf beetle (Lema cyanella).
• Green thistle beetle (Cassida rubignosa).

For more information about how biocontrol works, see What is biocontrol?

Community agrichemical control recommendations

Basic Growsafe certified: Foliar spray with 100ml glyphosate green per 10L of water.

Safety notes

Plant has spines.