Spear Thistle [Cirsium vulgare]

About the weed

It is a biennial dicotyledon, usually 30 - 150cm tall, though occasionally taller. It is very spiny and has a very deep tap root. The thistle flowers are reddish purple and usually occur singly on the flower stalk.

Key features

Plants: The stems have spiny wings and the young leaves have a hairy upper surface.

Biology

Spear thistle is common in arable fields. The plant dies in the autumn after flowering. It reproduces only from seeds, which have little dormancy and germinate in autumn or spring; the immature plants can overwinter as a rosette. Most of the seeds (up to 93%) are eaten by birds or small mammals.

Symptoms & Diagnosis

Life cycle

Seed longevity: >5 years

Seed weight: 2.5 mg

Seeds/head or capsule: 100

Seeds/plant: 8000

Treatment

Management

Being a biennial, it does not persist in arable rotations or routinely cultivated soils, but is encouraged by fallow or grass breaks or perennial crops. Seedlings are controlled by harrowing. Established plants are not easily controlled by mechanical means. MCPA herbicides can be used in cereal crops.