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Perennial Sowthisthle
Sonchus arvensis

Perennial sowthistle is a native of western Asia and Europe. It is common in cultivated areas, ditch banks, meadows, and neglected areas.

The stem is erect, stout, smooth, and unbranched except at the top. Upper leaves sessile and often unlobed, while lower leaves are considered short-petioled, and lobed. Leaves are alternate and light green; lower leaves can be 6 inches to 1 foot long, deeply cut, while upper leaves are slightly toothed. Perennial sowthistle can grow anywhere from 4 to 6 feet tall, reproducing by seeds and horizontal roots.  Rhizomes, horizontal underground stems, measure < 1 cm in diameter, usually 5-12 cm below the soil surface, and grow about 2 m or more in a single growing season.  One reason perennial sowthistle can survive cold temperatures is due to the fact that the roots can overwinter and survive temperatures to -16º C.

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Stems are hollow with clasping leaves at the base; there is no leaf petiole. Notice at the base of the stem the rounded basal lobes referred to as auricles. Leaves are irregularly lobed, with spines around the leaf margin.

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When broken, both the leaves and stem exude a milky latex. All plant parts are filled with a bitter, milky juice.

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Yellow, dandelion like flower heads can be 2 inches in diameter.  

Seeds are reddish-brown, ridged, and wrinkled with a tuft of fine white hairs.

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CONTROL

Biological

No biological control agents are available for perennial sowthistle, but both cattle and sheep have been seen graze the weed and reduce infestations in irrigated pastures. Herbicides are available for control.

Mechanical
Tillage implements that can work and bury the root fragments below 30 cm or leave them on the soil surface to dry out may reduce infestations. The best timing for cultivation to reduce stored root reserves is when plants are in the 6-9 leaf rosette stage. Repeated cultivation is needed for most infestations.

Grazing and repeated cultivation can help reduce perennial sowthistle stands by depleting root energy reserves. Cultivation is most effective when young shoots are at the 6-leaf rosette stage.

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