Idaho OnePlan recommends the website of the Idaho Weed Awareness Campaign as the best resource for up-to-date information about Idaho's noxious weeds, and their control.
Source for this page: Idaho's Noxious Weeds by Robert H. Callihan & Timothy W. Miller

BACKGROUND

Perennial sowthistle (Sonchus arvensis) is a native of western Asia and Europe. Its spreads both by seed and creeping roots, and it grows under a wide range of environmental conditions. Plants can be produced from root buds as deep as 2 feet, often resulting in large, dense colonies.

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DESCRIPTION

Perennial sowthistle has crowded, spatula-shaped to deeply lobedA cut into a leaf from the edge toward the center; greater than toothed, but not quite compound, dandelion-like leaves up to 10 inches long near the base of the plant. Stem leaves are much reduced, usually unlobed, and scarce; all leaves are prickly toothed along the marginsmargin: edge of the leaf. Stems are hollow, sparsely branched, and up to 6 feet tall. Both leaves and stems exude a milky latex when broken. Yellow, dandelionlike flower headsA group of flowers borne tightly together to 2 inches wide are borne from June until frost. The flower heads and their stems bear coarse, spreading, gland-tipped hairs. Seeds are reddish-brown, 1/8 inch long, flattened, ribbed, and tipped with white plumesA hairlike or featherlike structure, often on a seed. The plant has extensive horizontal roots.

DISTRIBUTION

Perennial sowthistle is found throughout the northern U.S., and in parts of California, Texas, Missouri, and North Carolina.

CONTROL

No biological control agents are available for perennial sowthistle, but herbicides are available for control.