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Smooth Sow-thistle

Botanical Name: Sonchus oleraceus
Other names: Annual Sow-thistle, Milk-thistle, Swine thistle
Family: Asteraceae

Annual, spreading by seed which have short plumes (pappus) of silvery-green hairs. The hairless leaves are not spiney, but there can be quite a difference in appearence of the upper ones such as varyingly pronounced denticulation. They are lobed and are arranged alternately on the upright hollow stem, which exudes a white sap when broken. They can be added to salads and the base of the mid-rib can have a reddish colouration when the plant is growing in full light.
There can be variation in the flower colour, but they are usually bright yellow and open from June to August. After self-pollination or by bees and hoverflies, the sepals close up again as the seeds mature, then reopen to release the pappus which carries them away.
Height - up to 90 cm.
The taproot is easily taken up on open ground and should not regrow if the basal growing point is removed. Regular hoeing should reduce the seedbank. Weedkillers to use:-
Dichlobenil prevents emergence of seedlings amongst established woody plants, for up to one year.
Paraquat, Diquat kills on contact.
Glyphosate, systemic action killing the whole plant.

Also the Prickly Sow-thistle the Perennial Sow-thistle have similar basal leaves and bright yellow flowers.

See also Wall Lettuce which has similar basal leaves.

Follow these links for further details on Weeds, Weed Removal and Weed Prevention.