Perennial sowthistle

Sonchus arvensis L.
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Status:
State Designated
•
Priority 4
Synonyms:
Creeping sowthistle, field sowthistle, moist sowthistle, milk thistle, swine-thistle, dindle

Description

Perennial sowthistle is an herbaceous perennial in the Asteraceae (daisy) family. It produces erect stems from basal rosettes that may reach 2 to 6 feet tall. These stems are smooth, hollow, and may be branched toward the top. Leaves are green, long, and occur alternately on the stem, but leaf shape may vary widely from oblong to lance-shaped, and lobed or entire. Leaf margins have small spines. Perennial sowthistle flowers from early to late summer. Flowers occur in small clusters at the ends of stems and branches. Flowers are composite flowers consisting of clusters of yellow petal-like ray flowers and resemble flat dandelion flowers. Perennial sowthistle has an extensive rhizomatous root system reaching up to 10 feet in depth. Seeds are small, reddish-brown, and have tufts of hairs or bristles that allow the seeds to be wind dispersed. All parts of the plant produce a thick, milky sap when broken. This sap is not toxic.

Origin and Spread

Perennial sowthistle is native to Europe, Asia, and North Africa. It was introduced into North America in the late 18th or early 19th century, likely as a seed contaminant. It creates dense infestations by spreading rhizomes and seeds and spreads to new locations primarily by wind-dispersed seeds. Perennial sowthistle may be found in a variety of areas but primarily prefers riparian and damp areas in pastures, landscapes, and gardens.

Management Options

Prevention strategies and cultural control strategies should be utilized as much as possible. Controlled grazing with sheep or cattle may be effective at preventing seed production and depleting root mass. There are not currently any biological control agents available for control of perennial sowthistle in Teton County.

Hand pulling and digging out of rhizomes is not recommended unless conducted routinely throughout the growing season because rhizome fragments are capable of resprouting. Mowing at regular, 3 to 4-week intervals can effectively deplete food stores in roots and prevent seed production. Do not mow while seeds are present. Tillage may be effective if rhizomes are buried at least 12 inches deep.

Larger infestations can be controlled with herbicides. Early to mid-summer treatments before bloom can be effective; fall treatments with systemic herbicides can also effectively kill the rootstock. Read the label before using any herbicide. Contact TCWP if you have any questions about application rates or how to use an herbicide.

Treatment AreaRecommended Herbicides
Range, Pasture, Natural AreasAminopyralid
Pasture where manure or hay will be used for compost2,4-D or dicamba
Lawn or landscape2,4-D + dicamba
Riparianglyphosate (aquatic label)

Additional Resources