APC (2020). The Australian Plant Census, Council of Heads of Australasian Herbaria, Available at: https://biodiversity.org.au/nsl/services/apc . [accessed 20/10/2020].
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Nodding Thistle (Carduus nutans) is an annual or, usually, biennial herb, initially forming a prostrate rosette, then ultimately growing into a robust erect plant up to 1.6 m tall. The rosette leaves are spiny, metallic green to grey-green with whitish mid-veins and margins, lanceolate (lance-shaped with the widest part nearest the base) to oblanceolate (lance-shaped with the widest part nearest the leaf tip) in shape. The first few leaves are only slightly lobed and have soft spines. Later rosette leaves are longer (to about 25 mm, rarely 50 mm), stiffer, more deeply lobed and with prominent stiff spines. Rosettes have stout taproots that may branch and penetrate soil to about 40 cm depth.
Erect stems (to 1.6 m tall) develop from the rosette, branching in the upper part, with hairs appearing cobwebby to woolly, and with spinose (spiny) wings forming along the stem from the base of the sessile stem leaves. The stem branches profusely 200 to 300 mm above the ground. Stem leaves are similar to the rosette leaves, are stem-clasping, and vary in size normally smaller than rosette leaves, 50-100 mm long vary. Leaves are light green or yellowish in young plants and grey-green, even dark green, with a prominent white central vein in older plants, deeply lobed. The margins are spiny and each lobe is surrounded by rigid spines a few millimetres long.
Solitary terminal flower-heads are purple to pink or rarely white, and form on the main stems and successively on the lateral branches. The largest flowering heads can be up to 60 mm in diameter. The heads droop or "nod" to one side, leading to the common name of Nodding Thistle. The middle and outer bracts surrounding the flower head are spine tipped. Each head consists of a large number of narrowly tubular flowers. Each flower being about 18-22 mm long. Larger, first-formed heads may each contain in excess of 500 flowers whilst later forming smaller heads may have up to 250 flowers. Flowers in spring, summer and autumn. Each flower produces a seed with many seeds produced on a flower-head.
The fruits or 'seeds' (cypselas) are smooth, pale brown, 3-5 mm long and ovoid in shape with a terminal but easily detached tuft of unbranched white hairs (a pappus) to 20 mm long (Popay & Medd 1990; Parsons & Cuthbertson 1992).
Recognition: This species can normally be recognised by the combination of the following characters; biennial herb, initially rosette, then ultimately growing into a robust erect plant up to 1.6 m tall; stem branches profusely 200 to 300 mm above the ground; [older] spiny leaves have a central white vein; best character is the single purple flower heads that nod, hence the common name 'Nodding Thistle'.
For further information and assistance with identification of Nodding Thistle (Carduus nutans) contact the herbarium in your state or territory.
Purple, pink or white.
Nodding Thistle (Carduus nutans) is found in open situations such as pasture, road edges and grasslands, in temperate regions of Australia with soils of moderate to high fertility and rainfall of 500 to 900 mm per year, on well-drained sites(DPI NSW 2019). The presence of disturbed sites in pastures and native grasslands at the end of summer favours its establishment. Nodding Thistle (Carduus nutans) has an absolute requirement for vernalization (chilling) before it can flower therefore requires cold winters (Popay & Medd 1990; Parsons & Cuthbertson 1992).
Other thistles occurring in southern Australia with purple or pink flowers and greenish leaves are the Slender Thistles (Carduus pycnocephalus and Carduus tenuiflorus) and Spear Thistle (Cirsium vulgare). Nodding Thistle (Carduus nutans) differs from all of these most obviously by its nodding flowerheads (see Navie 2004).
In Australia, Nodding Thistle (Carduus nutans) has proven to be an aggressive competitor of pastures. It occurs in dense patches and is not readily grazed by most stock because of its spiny foliage. Its presence also discourages animals from grazing other neighbouring pasture plants and it can affect the movement of stock.
Agriculture: In pastoral areas Nodding Thistle (Carduus nutans) forms dense patches of spiny plants and may occupy considerable areas of pasture out-competing desirable pasture species and reducing carrying capacity. The spines deter stock and thistle exudates restrict growth of nearby pasture (Popay & Medd 1990; Parsons & Cuthbertson 1992).
Seed production is high and seed longevity is habitat dependent being up to about 7 years in bare or cultivated ground and up to about 13 years in pasture (Popay & Medd 1990; Parsons & Cuthbertson 1992).
Native ecosystems: In native grasslands it is invasive in disturbed areas along tracks and areas of animal disturbance and can persist if unchecked (Popay & Medd 1990; Parsons & Cuthbertson 1992).
Urban areas: May invade roadsides and grassy areas. Known to have invaded a grassy air strip in Western Australia.
Nodding Thistle (Carduus nutans) reproduces only by seed and a single plant can produce up to 120,000 seeds. The seed develops with a pappus (a tuft of silky hairs) on one end but this easily falls off and does not aid dispersal. Most seed falls from the head within 2 m of the base of the plant. Wind does not have a major role in dispersal and nodding thistle seed are usually not blown more than 10 metres.
Longer distance dispersal has been through human activity, on machinery, in soil, on livestock, in hay and as a contaminant of agricultural seed (Popay & Medd 1990; Parsons & Cuthbertson 1992; Woodburn & Sheppard 1996). Seed may be carried in water.
Nodding Thistle (Carduus nutans) was introduced to Australia repeatedly from the 1940s as a contaminant in pasture and crop seeds, first being recorded as established from Oberon, New South Wales in 1950. In the 1960s it was declared a prohibited contaminant of imported seed (Woodburn & Sheppard 1996; Parsons & Cuthbertson 1992).
It is difficult to control because of its long flowering season, prolific seed production, the longevity of its seed bank, a variable life cycle, and the ability to germinate at any time of the year provided there is moisture available. The best defence against invasion of Nodding Thistle (Carduus nutans) on agricultural lands is maintaining healthy perennial pasture with good ground cover in summer going into autumn to prevent seedling establishment. With existing infestations control will depend on acreage infested and weed density.
Chemical control: Herbicide application in springtime when the first buds are obvious in the centre of the rosette has been shown to be effective. The least satisfactory time of application of herbicides is mid-winter, and when the stems are elongating (Parsons & Cuthbertson 1992; Dellow 1996). Springtime non-lethal herbicide application combined with grazing is the best of the integrated strategies (Shea et al. 2006).
An infestation may contain plants at various stages, including seedlings, small rosettes, large rosettes, flower-stem growth, and full flower and the type of herbicide used will depend on the stages of growth in an infestation. 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.
Resistance of Nodding Thistle (Carduus nutans) to some herbicides has been shown to develop in New Zealand with continued use. The only effective means of avoiding the development of resistance is to reduce dependence on herbicides for control, especially by using pasture management to reduce weed establishment in summer going into autumn (Harrington 1996). Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au.
Non-chemical control: Physical control: Hand remove isolated plants or small populations through spring and early summer.
Cultivation of the soil will encourage germination that can be followed up with herbicide application.
Grubbing: where the number of plants involved is small, removal by grubbing is feasible. The thistle should be grubbed out ( This method requires weeds to be dug out using a mattock or chip hoe) to a depth of at least 5 cm.
Slashing: The Slashing or cutting of plants in bud or then early flowering stage can be used to delay flowering or seeding, but will likely result in additional stem growth (coppicing) from the stem or rootstock, and must be followed up by measures to kill the whole plant. If the plant is in full flower, heads should be collected and burnt since seed may mature on the cut stalks.
Grazing management, Grazing by goats has been shown to be effective against Nodding Thistle (Carduus nutans) as they selectively graze flower-heads and heads setting seed and thus can reduce overall seed-set. They rarely graze rosettes. Sheep grazing is an ineffective control method (Holst & Allan 1996). A combination of seasonal 'crash-grazing', in either autumn or spring, at up to four times the normal grazing pressure, combined with biological control agents, is highly effective (Shea et al. 2006).
Biological control: Nodding Thistle (Carduus nutans) has also been recognised as a target for biological control through a cross-jurisdictional government process. This allows activities to be undertaken to develop effective biological controls. Three biocontrol agents (one a Root-crown Weevil Trichosirocalus mortadelo, and two flowerhead feeding insects Urophora solstitialis and Rhinocyllus conicus) have been released in an effort to control Nodding Thistle. The Root-crown Weevil is the most effective as it attacks a life stage critical to the thistle's invasive success in Australia while the seed feeders do not (Shea et al. 2006).
Populations of Nodding Thistle (Carduus nutans) always contain plants of mixed ages and sizes, and all plants require low temperature vernalization (exposure to cold) at the rosette stage to initiate elongation and flowering. Most plants germinate in autumn, form a rosette which sits over winter and then as the weather warms the stem elongates. Flowering is from November through summer to as late as the following autumn. After seed is shed the plant dies (Groves & Kaye 1989; Popay & Medd 1990; Parsons & Cuthbertson 1992).
Large rosettes need shorter vernalization periods than do small rosettes so plants forming a large rosette before the onset of winter will flower earlier the following summer whereas small rosettes will only flower if they have received adequate length of cold If not they may continue through the summer as a rosette, experience more cold the following winter and flower the second summer. Any seeds not germinating and establishing a rosette until spring may flower in the following autumn if an adequate cold period is experienced, or the rosette may carry through the following winter and flower in the second summer (Groves & Kaye 1989; Popay & Medd 1990; Parsons & Cuthbertson 1992).
ACT, NSW, QLD, TAS, VIC, WA
Nodding Thistle (Carduus nutans) is found commonly on the Northern, Central and Southern Tableland areas of New South Wales, and sporadically in south-eastern Queensland, Victoria and Tasmania where control has been largely effective. Small occurrences have been eradicated in Western Australia (Popay & Medd 1990; Parsons & Cuthbertson 1992).
Nodding Thistle (Carduus nutans) originated in Europe, northern Africa, Asia Minor and Asia (i.e. Eurasia) (Navie 2004).
ACT, NSW, TAS, VIC, WA
Carduus nutans L. subsp. nutans
Musk Thistle. Note: Carduus nutans and C. thoermeri often are referred to under the same common name: Nodding Thistle.