Sonchus asper is a dicotyledonous annual or biennial herb in the family Asteraceae (Grubben & Denton, 2004). Plants can grow up to 2 metres in height. It has a ridged, glabrous (hairless) central stem that is simple or branched and is pentagonal in cross section. The tap root is usually unbranched (Hutchinson et al., 1984). Egg-shaped cotyledons are borne on petioles and are approximately 3 to 8mm long. Cotyledons and young leaves have a whitish coating. Young leaves form a basal rosette, sometimes causing them to be confused with thistles. Mature leaves that occur on the flowering stem are alternate and have rounded lobes that clasp the stem and measure 4-30cm x 1-9cm (Virginia Tech, undated). All leaves are glabrous, oblanceolate in shape, bluish green in colour and have prickly margins. Leaves and stems emit a milky sap (latex) when damaged.\r\n

Inflorescences (capitula) are 4-5mm in diameter, yellow in colour and occur in clusters at the end of stems. Each capitulum contains 25-150 ligulate bisexual yellow florets (Hutchinson et al., 1984). Fruits are brown, wrinkled achenes 2.5-4mm long and 1.5mm wide. Achenes have 3 (or rarely 4-5) longitudinal ribs on each face (Hutchinson et al., 1984). Mature seeds have a white feathery pappus (8mm long) that collectively form a white puff ball, similar to dandelion (Grubben & Denton, 2004).

Sonchus asper is an annual or biennial herb (Cuevas Marticorena & Cavieres 2004). It reproduces by seed, and overwinters in the vegetative phase as rosettes or as seeds (Hutchinson et al., 1984).

Sonchus asper is eaten cooked and raw in salads in Africa, Madagascar(Grubben & Denton, 2004) and in the Mediterranean (Leonti et al., 2006) Its roots, stem, leaves, juice, latex or whole plant has also been used to treat a vast variety of conditions, ailments and diseases. These include treatment of wounds, boils, asthma, bronchitis, gastrointestinal infections, malaria, venereal disease and many more (Reviewed in Khan et al., 2010). The latex has also been used to treat warts (Grubben & Denton, 2004). Chemical analysis of S. asper has confirmed that it contains large quantities of phenolic compounds, flavonoids, ascorbic acid, carotenoids and a variety of other antioxidants. Khan et al. (2010) confirm that S. asper extract protects rats from renal damage associated with CCl4 (a source of free radicals).

Sonchus asper can grow on a variety of soil types including white to grey sand, brown clayey loam, black sandy loam and black clayey peat (FloraBase, 2010). It can grow in dunes, valleys, seasonally wet areas, watercourses, lakes, wetlands (FloraBase, 2010), pastures, hay fields, orchards, roadsides and other disturbed sites (Virginia Tech, Undated).\r\n

S. asper prefers well drained, slightly acid to alkaline soils, but are tolerant of saline soils (Lewin, 1948 in Hutchinson et al., 1984). Their range in Canada suggests a broad tolerance to climatic variation (Hutchinson et al., 1984). Occurs from 750-2550m in altitude (Grubben & Denton, 2004)

Sonchus asper flowers are insect pollinated by solitary bees and fly species. Flowers are also self compatible and seeds are produced through self pollination and fertilization (Hutchinson et al., 1984). An average of 23,000 achenes (seeds) are produced per plant (Salisbury, 1942 in Hutchinson et al., 1984). Seeds are primarily dispersed by wind, although they have been found attached to clothing (Ridley, 1930 in Guertin, 2003) and in feathers and fur of birds and animals (Zollinger & Parker, 1999 in Guertin, 2003). Seeds are viable for 1 to 3 years, depending on conditions. Sonchus spp. seeds may also be dispersed by animals being passed through the digestive tract.

Sonchus asper is a major problem in winter crops and in tillage systems throughout southern Australia, South-East Queensland and Northern New South Wales (CSIRO, 2007).\r\n\r\n

S. asper is also an important alternative host of pests and diseases of crops (CSIRO, 2007). In Canada S. asper acts as an alternate summer host to economically important aphids, which are vectors of “yellows” virus diseases. They may also serve as hosts for nematodes which attack cultivated plants (Hutchinson et al., 1984). It is also likely to be an important host for downy mildew (Bremia lactucae), one of the worst diseases of lettuce which is an important vegetable crop worldwide (Vieira & Barreto, 2006).

Physical Control: Small or isolated populations may be manually removed while plants are young, prior to seed set. The taproot must be removed, as resprouting can occur if left in the soil (Elkhorn Slough National Estuarine Research Reserve, 2000 in Guertin, 2003). Slashing is often ineffective as flowers continue to be produced (FloraBase, 2010). Regular cultivation of plants, every three months or so, will stimulate germination and can lead to a diminished seed bank. This will also drain food reserves stored in the roots and cause death (Zollinger & Parker, 1999 in Guertin, 2003). Mulching and soil sterilisation methods can complement other management efforts (Elkhorn Slough National Estuarine Research Reserve, 2000 in Guertin, 2003).\r\n

Grazing: Grazing of Sonchus spp. by cattle and sheep effectively suppresses infestations in pastures, and weakens plants allowing other control methods to be more effectively used (Zollinger & Parker, 1999 in Guertin, 2003). They also make excellent feed for livestock.\r\n

Chemical Control: For control of Sonchus spp. (asper and oleraceus), a pre-emergent herbicide containing isoxaben can be used, herbicidal soaps when the plants are young, or glyphosate when plants are mature. Zollinger and Parker (1999 in Guertin, 2003) recommend 2,4-D, clopyralid, dicamba, glyphosate, and picloram for control of Sonchus spp., while Rice (1992 in Guertin, 2003) 2,4-D, DCPA, diethatyl-ethyl, MCPA, amitrole, atrazine, bromoxynil, chlorsulfuron, dicamba, dichlorprop & 2,4-D, diuron, glyphosate, isoxaben (Snapshot), norflurazon, oryzalin, oxyfluorfen, paraquat, Ornamental Herbicide II, napropamide, simazine and tebuthiuron.\r\n

S. asper has developed resistance to chlorsulfuron in southern Queensland and northern New South Wales (Adkins et al., 1997 in Chauhan et al., 2006)atrazine (CSIRO, 2007) and acetolactate synthase inhibitors (metsulfuron-methyl, thifensulfuron-methyl, tribenuronmethyl) (Weedscience.org, 2003 in Guertin, 2003). Apparently spot spraying of Lontrel® 10ml/10L with a wetting agent can be used to control the plant, preferably at the rosette stage (FloraBase, 2010).\r\n

Biological Control: Biological agents are currently being researched as a possibility for managing S. asper and other Sonchus species in Australia (CSIRO, 2007). Sonchus species have previously been the target of biological control in Canada (Peschekn, 1984 in CSIRO, 2007). Preliminary surveys for biological control agents have been made in southern France and northern Europe (Scott & Jourdan, 2005; Peschken, 1984). Currently the rust fungus Miyagia pseudosphaeria and an unidentified eriophyid mite species are two widespread organisms in Australia with potential for control. The CSIRO project will focus on determining the impact of these potential control agents on related native Australian species ( Sonchus hydrophilus and Actites megalocarp and on weedy S. oleraceus and S. asper (CSIRO, 2007).