Soldier thistle - Department of Primary Industries

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Common name:	soldier thistle
Scientific name:	Picnomon acarna (L.) Cass.
Other scientific name/s:
Other common name/s:

Plant status

Catchment management authority boundaries

		Regionally prohibited in the North Central, Port Phillip and Western Port Catchments
		Regionally controlled in the Goulburn Broken and North East Catchments
		Restricted in the Mallee, Wimmera, Corangamite, Glenelg Hopkins, West Gippsland and East Gippsland Catchments

Plant images

Plant biology

Appearance	Herbaceous plant - Forb (flowering herbaceous plant - not a grass)
Description	Soldier thistle is an erect annual herb growing to 1 m high. Yellow-green in appearance due to numerous yellow spines on the leaves.
Stems	Stems of soldier thistle are ranched with spiny wings and dense white hairs. They are woolly in appearance.
Leaves	Soldier thistle leaves are covered with fine white hairs and yellow spines, 1-1.5 cm long. White hairs on the leaves give them a woolly appearance. Rosette leaves grow to 30 cm long while stem leaves alternate and are long and narrow, about 1-1.5 cm in length.
Flowers	Soldier thistle has pink or purple flower heads, growing 2-4 cm long and can be solitary or in groups at the end of branches. Flowers are formed in late spring from September to November with the plant flowering in early summer.
Seeds	The seeds of soldier thistle are smooth and shiny with a detachable parachute of bristles on one end about 4-6 mm long. Seed germinates mainly in autumn, but has been seen to germinate after sufficient summer rainfall in disturbed areas.

Growth and lifecycle

Method of reproduction and disperal

Wind is the main method of dispersal for this weed. Seeds can disperse over short distances and whole plants can also be blown around after breaking off at the base. Seeds can also be carried on animals, vehicles, machinery and in water.

Rate of growth and spread

Soldier thistle grows rapidly in spring, particularly on heavy red-brown soil and spreads fast in degraded areas with little competition. It can compete with crops in favourable conditions.

Seedbank propagule persistence

A small percentage of solder thistle seeds can remain viable in the soil for several years. Plants may appear on recently cultivated areas where there has been no seeding for several years.

Preferred habitat

Soldier thistle prefers semi-arid to sub humid areas of temperate regions on dry sandy or stony soils. It is a weed of roadsides, channel banks, neglected areas and occasionally cereal crops and pastures in areas with an annual rainfall of 300-600 mm.

Distribution

In Victoria, soldier thistle is found in the Mallee and northern regions of the state.

Growth calendar

The icons on the calendar below represent the times of year for flowering, seeding, germination, the dormancy period of Soldier thistle and also the optimum time for treatment.

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Flowering
Seeding
Germination
Dormancy
Treatment

Impact

Agricultural and economic impacts

Well established infestations of soldier thistle can compete with crops and choke harvesting equipment. The sharp spines of the plant can injure animals and are generally avoided by stock.

Management

Recommended treatment

Application of a registered herbicide
Physical removal

Important information about prescribed measures for the control of noxious weeds

Other management techniques

Cultivation of the soil in which young African boxthorn plants grow may also support its management after implementing the prescribed measures above.

References

Parsons,W.T. and Cuthbertson, E.G. 2001, Noxious weeds of Australia, 2nd edn, Inkata Press,Melbourne & Sydney.

Department of Primary Industries, Soldier Thistle Regionally Prohibited Weed Fact Sheet, February 2010