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Botanical name: Sonchus oleraceus

Family: Asteraceae

Other common names: annual sowthistle, colewort, field sow-thistle, hare’s lettuce, hare’s thistle, milk thistle

Common sowthistle is an annual and sometimes biennial herb, 40-150 cm tall, containing white latex in all plant parts. Mature leaves are thin, soft and dark-green in colour with irregularly-toothed margins and increasingly lobed with maturity. Leaves can rosette at ground level and lower leaves can be up to 25cm long. The inflorescence is a terminal panicle, with yellow flowers that are 5-6mm in diameter. Flowers are insect pollinated by bees and flies, and seeds are produced through both selfing and outcrossing. The small light seeds are easily dispersed by wind and water. Common sowthistle grows in a wide variety of environments and soils (including potting mix, saline conditions and shallow soils). It is commonly seen on roadsides, cultivated land, gardens, construction sites, sand dunes, logged or burned areas and riparian zones. Common sowthistle grows and flowers quickly, producing copious amounts of seed. Resistance to ALS-inhibiting herbicides, such as chlorsulfuron and metsulfuron-methyl have been reported in Australia.

A variety of insects are known to feed on Sonchus species, including aphids, leaf-mining and gall-forming flies, lepidoptera, mites, and nematodes. Common sowthistle is a host to Bremia sonchi (downy mildew), Bremia lactucae (downy mildew lettuce), Golovinomyces cichoracearum var. cichoracearum (powdery mildew), Coleosporium tussilaginis f.sp. sonchi (rust fungi), Podosphaera fuliginea (powdery mildew), Miyagia pseudosphaeria (rust fungi), Puccinia littoralis (rust fungi), Alternaria sonchi (Alternaria leaf spot) and Aecidium sonchi (rust fungi). Viruses hosted by common sowthistle plants include lettuce necrotic yellows virus, beet yellow stunt virus (affecting sugar beets as well as lettuce), watermelon mosaic virus, and tomato spotted wilt virus (UNE). Common sowthistle is also a host for the lettuce aphid (Nasonovia ribisnigri) and the lettuce root aphid (Pemphigus bursanus) (UNE). Large sowthistle aphid (Uroleucon sonchi. Lantana mealybug (Phenacoccus parvus (Swarbrick). It has also been noted as an alternative host of the fungal pathogens black root rot (Chalara elegans) and corky rot (Rhizomonas suberifaciens) (UNE). Common sowthistle is a known host plant for Green vegetable bugs (NZAC FACT SHEET). Green vegetable bugs were also recorded on common sowthistle in macadamia orchards (Jones).