Nodding Thistle

(Carduus nutans)

What is nodding thistle?

Nodding thistle is a serious pasture weed.

Nodding thistle is a declared weed under the Tasmanian Weed Management Act 1999. The importation, sale and distribution of nodding thistle are prohibited in Tasmania.

How to identify nodding thistle

Nodding thistles are normally biennial plants (living for two years). The thistle grows into a rosette (a whorl of leaves close to the ground) in its first year. In its second year, the rosette produces one or more spiny stems up to 1.5 m in height and often branched towards the top.
The flowers are red-purple in colour and around 50 mm across. As the flower head develops the stem below the head bends, resulting in the typical 'nodding' appearance of this thistle.
In some areas in Tasmania, nodding thistles can grow through from the rosette stage to flowering in the one season, thus behaving as an annual.
For help in identifying thistles in Tasmania, see Identifying Thistles in Tasmania and search the Dennis Morris Weeds and Endemic Flora database for nodding thistle illustrations. If you are still in doubt about the thistle you are dealing with, contact Biosecurity Tasmania on 03 6165 3777 for help.

Nodding thistle in Tasmania

Nodding thistle occurs in small patches in most parts of Tasmania, mainly in the north and north east of the state and through the Midlands.
Nodding thistle prefers open situations on richer soils receiving good rainfall. Nodding thistles are an aggressive competitor with pasture. Rosette diameters exceeding one metre are common so losses in productivity through competition with pasture grass can occur even at low weed densities. Plants can grow up to two metres tall and dense stands of nodding thistle can also reduce the accessibility of pasture to stock.

What is the legal status of nodding thistle in your area?

The legal responsibilities of landholders and other stakeholders in dealing with nodding thistle are laid out in the Statutory Management Plan for Nodding Thistle.
Use Table 1 (Zone A municipalities) and Table 2 (Zone B municipalities) in the Statutory Management Plan for Nodding Thistle to find out whether your area falls in an eradication or containment zone.

Detailed management and control guidelines for nodding thistle can be found in the Nodding Thistle Control Guide. Refer also to Herbicides for Nodding Thistle Control.

Thistle Identification Poster

Pest Genie

APVMA

Nodding Thistle Control Guide

Do

Plan your control program, this will save time and money in the long-run.
Use cultivation to eradicate a mature nodding thistle infestation.
Follow up cultivation by treating any nodding thistles that germinate in the crop.
Carefully time your use of herbicide for best results (see Herbicides for Nodding Thistle Control for more information).

Don't

Don't start your control program without first planning your approach.
Don't rely on just cutting and slashing - thistles will re-sprout from cut stems and rootstock.

Spread of nodding thistle

Seed is the only means of spread. A single plant has up to 120,000 seeds.
Seed may be carried as a contaminant of produce seed and hay, on vehicles and machinery, and in water and soil. Wind does not have a major role in dispersal and nodding thistle seed are usually not blown more than 10 metres.

Physical removal

Slashing and cutting of plants at the bud or early flowering stage can be used to delay flowering or seeding. However, this will usually cause 'coppicing' from the stem or rootstock, and must be followed up by measures to kill the whole plant.
Where the number of plants involved is small, removal by grubbing is feasible. The thistle should be grubbed out to a depth of at least 5 cm.
If the plant is in full flower, heads should be collected and burnt since seed may mature on the cut stalks.

Cultivation

Control of nodding thistle is best achieved by adequate cultivation of the site.
Ploughing and preparation for a crop will remove the germinated thistles, leaving a reserve of seed in the soil, which may germinate to produce thistles which will need to be dealt with in the crop.
Nodding thistle seed can remain dormant in the soil for 10 years or more. This dormant seed may germinate as a result of cultivation.

Biological control

Biological control is the use of living species, usually an insect, mite or disease, to control a weed.
Three biological control agents have been trialed or released in Tasmania to help control nodding thistle: the thistle-head weevil, seed-fly, and rosette weevil.
For more information on biological control programs in Tasmania contact the Tasmanian Institute of Agriculture.

Chemical control

A number of herbicides are registered for use on nodding thistle in Tasmania (see Herbicides for Nodding Thistle Control for more information).
An infestation may contain plants at various stages, including seedlings, small rosettes, large rosettes, flower-stem growth, and full flower. The type of herbicide used will depend on the stages of growth in an infestation (see Herbicides for Nodding Thistle Control for more information).
The best time to spray nodding thistle is when the plant is in the seedling and small rosette stage.
Control of an infestation in pasture may require spraying in spring and autumn.

Herbicides for Nodding Thistle Control

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