How to Manage Pests

Identification: Weed Photo Gallery

Annual sowthistle

Scientific name: Sonchus oleraceus (Sunflower Family: Asteraceae)

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Annual sowthistle is a widespread winter or summer annual broadleaf plant. It is abundant in California to about 4900 feet (1500 m) and is commonly found in California's Central Valley and coastal areas where it grows year-round. Annual sowthistle inhabits agricultural land and other disturbed locations. It can harbor pests that are economically important to vegetable and fruit crops. Such pests include lettuce aphid, Nasanovia ribis-nigri, lettuce-root aphid, Pemphigus busarius, green-peach aphid, Myzus persicae, and nematodes. All are potential vectors of plant viruses.

Habitat

Crop fields, orchards, vineyards, pastures, riparian areas, yards, gardens, roadsides, and disturbed sites.

Seedling

Species are not easy to distinguish at the seedling stage. Cotyledons (seed leaves) are egg shaped to narrowly football shaped, hairless, short stalked and about 1/6 to 1/3 of an inch (4–8 mm) long. The first leaf is egg shaped, sparsely hairy, and the leaf edge is lined with backward pointing teeth. Leaves are alternate to one another along the stem.

Mature plant

Plants are coarse, erect, and can reach about 4-3/5 feet (1.4 m) in height. The stem is smooth, thick, hollow between stem joints (nodes), and secretes a milky sap when cut. The leaves are hairless somewhat bluish green. The upper leaves are smaller than the lower leaves, stalkless, and clasp the stems with clawlike basal lobes. Lower leaves are usually about 4 to 8 inches (10–20 cm) long, with a tapered or winged base, and are deeply lobed. The terminal leaf lobes are much larger than the lateral lobes.

Flower

Flowering generally takes place in the spring and summer and under favorable conditions, year-round. Flowers cluster at the stem tips to form daisylike flower heads. When closed the flower heads are urn shaped. Flower heads mature into white, fluffy seed heads, although not ball-shaped like in dandelions.

Fruit

Fruit are football to egg shaped, flattened, and tiny—about 1/10 to 1/6 of an inch (2.5–4 mm) long. Attached to the fruit is a tuft of numerous, soft, fine, hairs.

Reproduction

Reproduce by seed.

Related species/Similar looking plants

Blessed milkthistle
Spiny sowthistle

More information

• Broadleaf ID illustration
• Calflora's distribution map
• See UC IPM's Pest Management Guidelines for agricultural information