Nodding thistle: declared pest

Page last updated: Thursday, 10 October 2019 - 12:29pm

Please note: This content may be out of date and is currently under review.

Nodding thistle (Carduus nutans) is a declared pest in Western Australia (WA). This article describes the nature of the plant with links to requirements land owners/occupiers must adhere to, pest control methods and how to search, detect and report it.

Form: herbaceous — annual
Status: eradicated from WA

Appearance

Biennial, tap-rooted thistle, native of Europe, Asia and North Africa, growing to 2.5 metres tall; a common weed in grasslands in south-eastern Australia; the only known population in Western Australia has been eradicated.

Stems: spiny and winged except below the flower head.

Leaves: deeply lobed and spiny margined. Rosette leaves to 50 centimetres long, often with whitish mid-veins ending in a rigid spine about three millimetres long.

Flowers: large purple heads (2.5-5 centimetres across) that droop down or "nod" at maturity; flower head bracts end in a strong, sharp spiny tip. Flowers mostly spring to autumn.

Seeds: grey to yellowish-brown, three to four millimetres long, slightly curved, marked with longitudinal lines and faint dots. Pappus 15-25 millimetres long.

Online weed identification training

Login or set up a new account on DAFWAs online training site to access:

Agricultural and economic impact

Nodding thistle can invade pastures. If not controlled it will form dense patches that greatly reduce carrying capacity as the spiny plants are not grazed by stock.

Declared pest category

The Western Australian Organism List (WAOL) contains information on the area(s) in which this pest is declared and the control and keeping categories to which it has been assigned in Western Australia (WA). Use the following WAOL link to reach the declaration and declaration map for: nodding thistle.

Requirements for land owners/occupiers and other persons

Requirements for land owners/occupiers and other persons if this pest is found can be sourced through the declared plant requirements link.

Search > detect > report

Detectability: hard to find. In its early growth, nodding thistle is likely to be confused with other thistles that are well established in the South West Land Division, particularly spear thistle (Cirsium vulgare). It can be distinguished from other thistles when the flowers mature as they droop or ‘nod’ whereas other thistles have flowers that are more-or-less upright. Nodding thistle is quite robust and taller than other closely related species present in WA, up to 1.6 metres tall, where slender thistle (Carduus pycnocephalus) and sheep thistle (Carduus tenuiflorus) have relatively slender stems and both only get to about 1m tall.

Who should look for it: owners/managers of grass airstrips, particularly in the higher rainfall parts of the South West Land Division, and anyone who uses these airstrips. Owners of land that had Karoo canola planted in 1996 (as it had low levels of nodding thistle seed).

When to find it: nodding thistle is most conspicuous when the flowers have matured, usually in late spring and summer. If nodding thistle becomes established, rosettes could be potentially found at any time of year.

Where to find it: nodding thistle has only been found once in WA, on a grass airstrip used by spray planes from the Eastern States. While nodding thistle prefers calcareous soils and nitrogen rich soils, it can also grow on poor or acid soils. It may be found on properties where Karoo canola was planted in 1996. If it becomes established, nodding thistle is most likely to take off in improved pastures, where top-dressing of pastures has occurred, and in areas that are bare for all or part of the time, such as fencelines and around troughs. It is most likely to become established in the higher rainfall parts of the South West Land Division.

Report: this pest to the Pest and Disease Information Service using the contact details given below or by using the MyWeedWatcher smartphone and tablet application or online reporting tool.

Control method

Control methods for this declared plant can be found through the nodding thistle control link.

Management calendarTable displays: Search Nov-Mar. Germination Feb-May. Actively growing Mar-Sep. Flowering Dec-Mar. Fruiting: Jan-Mar. Treatment Apr-Sep. Manual removal Jan-Dec.

 

Contact information

Pest and Disease Information Service (PaDIS)
+61 (0)8 9368 3080