Common Sowthistle (Sonchus oleraceus): Weed management guide for Australian vegetable production

Abstract

<p><b>Common sowthistle (<i>Sonchus oleraceus</i>) is an annual herbaceous plant, growing between 0.2 m and 1.5 m in height.</b></p> <p>Figure 1 includes a series of photos of common sowthistle at different life stages, from a young seedling through to a mature flowering plant, including images of the flowers and seed.</p> <p>Common sowthistle initially forms as a rosette, up to 25 cm in diameter, before growing as an erect plant commonly 1 m in height. Stems are circular, green to purple, hollow, and produce a milky sap when cut. Lower leaves are smooth, thin, and lance-shaped, while upper leaves are generally smooth although can be hairy. Upper leaves can show considerable variation in shape, but are generally bluish-green with irregularly-toothed margins ending in small soft spines. Leaves can be between 6 cm and 35 cm in length. The plant has a long, slender pale taproot that is usually branched.</p> <p>Flowers are light yellow in colour, 10 to 15 mm in diameter, with many narrow petals. Fruit (forming at the base of the flower) is wrinkled, tapers at the base, and produces fine white cottony hairs after flowering.</p> <p>At its early growing stages, common sowthistle is almost indistinguishable from prickly sowthistle (<i>Sonchus asper</i>), a weed that is also common in Australian vegetable farms and has much the same impacts as common sowthistle. However, as a larger plant, prickly sowthistle is distinguishable from common sowthistle by its leaf form, which is thicker, more curled and with much more significant spines along the leaf margins (Figures 2 and 3). Management of the two species will largely be the same.</p>