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Nodding Thistle

Nodding thistle plant

Nodding thistle bud

Nodding thistle rosette

Black thistle plant

Black thistle flower

Black thistle rosette

Scotch thistle

Variegated thistle1

Variegated thistle2

Variegated thistle3

Slender thistle plant

Slender thistle rosette

Winged slend thistle

Saffron thistle1

Mexican poppy flower

Mexican poppy rosette

Wild teazel

Blue devil plant

Blue devil, leaves

 


BOTANICAL NAME:

Carduus nutans


Family:

Asteraceae (daisy family)

Status:

Nodding thistle is declared noxious in the Southern Tablelands and South East Region in all LCAs except for Illawarra, in class 4.

Description

Most thistles are erect single-stemmed or branching biennial herbs ranging from 30cm to 2m high depending on species and growing conditions. They are characterised by having long spines on the leaf margins and stems. The plant begins life as a rosette, from which an elongated flowering stem arises. Flower heads consist of numerous small flowers clustered into cylindrical or hemispherical heads at the branch tips, and surrounded by spiny bracts. Flower colour is pink to purple for most of the species found in the region, except for a few with yellow flowers.

Nodding thistle is distinctive in having the purple flower heads bent over at right angles to the stem. The rosette leaves are narrow, grey-green, deeply lobed right to the central vein (midrib) and densely spiny on the margins.

For additional thistle photos, check the entries for Scotch, star thistle and soldier thistle.

preferred habitat and impacts


Thistles are invasive weeds of pasture, reducing carrying capacity. The broad flat rosette habit in the early stages of growth smothers surrounding grass plants, and the density of stands which can occur after disturbance such as over-grazing or cultivation can choke out all other vegetation. Unpalatable to stock because of the spines, they are favoured by heavy grazing. The spiny nature of thistle plants restricts stock and human movement in infested pasture.

Thistles are a more troublesome weed in the drier tablelands and slopes of southern NSW than on the coast, and more species are present in these areas. Black or spear thistle is the most common thistle found on both the coast and the tablelands, but other thistle species are quite uncommon on the coast.
Thistles are also environmental weeds, invading grasslands and grassy woodlands and occasionally moving into forest where there is sufficient soil moisture for them to overcome the competitive effect of the trees, particularly along road edges.

dispersal


Seed is generally wind-blown, and moved around in soil and on animals, vehicles and machinery. Contaminated hay and agricultural seed are also a source of infestations. The degree of wind movement of thistle seed varies with the species. Although all have a parachute of bristles to help keep the seed aloft, in some species such as nodding thistle this breaks off readily and does not assist much with dispersal. In other cases such as black thistle, seed can drift for long distances on the wind.

look-alikes


All thistles are broadly similar in appearance and nodding thistle is distinguished by its drooping flower heads. Some plants have a resemblance to thistles although they are not closely related.
The weed Mexican poppy (Argemone ochroleuca) has thistle-like spiny foliage which is silvery grey in colour. It is in the poppy family, and has a cream coloured poppy flower and a prickly seed capsule which splits at the top to release numerous small black seeds. It grows to about 1m high. Wild teazel (Dipsacus fullonum) has more elongated cylindrical heads of mauve flowers with long spiny bracts at the base, and short prickles on stems and the vein on the leaf underside, but not on leaf margins. It is also a weed.

There is a native plant with thistle-like foliage and flower heads surrounded by long spiny bracts, the blue devil (Eryngium rostratum). It is a plant of native grasslands and grassy woodlands on the tablelands and slopes, and is very unlikely to be found on the coast. It has blue flowers in branched heads, and when these dry off they could look similar to dead thistle plants.

control


Small infestations of thistles can be chipped out, but may regrow if the cut is not made deeply enough. Hold the top of the plant down to the ground with one foot to get the spiny leaves away from your hands while chipping, or catch them while still in the rosette stage, when they are very much easier to cut. Spot spraying or boom spraying can be used for larger infestations, perferably with a selective herbicide which will not remove grass cover. Slashing can be a temporary measure to delay seeding, but plants will regrow from the base and viable seed may form on the cut plants if slashing is done after flowers have been fertilised. Seed is long-lived in the soil (up to 10 years), so prevention of seeding is important.

Goats and donkeys can help reduce seed-set by eating the flowers. Various biological controls have been trialled (see some information at the following web address: www.ento.csiro.au/research/rr97-99/weedm_projects.html )





Nodding thistle biocontrol pdf Nodding thistle biocontrol pdf 449.1 KB