Perennial Sowthistle

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Description:

PERENNIAL SOWTHISTLE - Asteraceae - (Sunflower family)

A perennial, spreading from horizontal rhizome-like roots. Plants are usually 2 to 4 feet tall, succulent, and exude a milky juice when injured. Leaves have a clasping base and mildly prickly margins which vary from deeply toothed to nearly entire. Upper leaves are fewer and much smaller than the basal ones. The flower head is 1 to 2 inches wide, and rich yellow in color.

Numerous gland-tipped hairs on involucre bracts and flower stalks help distinguish this species. Seeds are dark brown, prominently ridged and wrinkled, with a tuft of soft white pappus bristles.

Perennial sowthistle is a native of Europe or Eurasia. It is widely distributed in North America, and considered noxious in many states and provinces. It is common in gardens, cultivated crops, ditchbanks, and fertile waste areas where adequate water is available. Marsh sowthistle (listed by various authors as S. uliginosus Bieb., S. arvensis L. ssp. uliginosus (Bieb.) Nyman, or S. glabrescens Jord.) is a similar perennial; the most important difference being a lack of gland-tipped hairs.

(Courtesy of Weeds of the West)

Growth Habit: Perennial, up to 4` tall.

Leaves: Prickly serrations on margins, may be deep lobed, narrow at base. Upper leaves clasp stem. Alternate, usually crowded on lower ½ of stem.

Stems: Erect, finely grooved, hollow between joints, milky juice.

Flower: Bright yellow, flat topped, clustered, 1 to 2" in diameter

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Roots: Creeping horizontal roots, give rise to new shoots at joints. Yellowish white with milky juice.

Seeds: Reddish brown, 1/8" long, 5 to 7 lengthwise ribs.

Other: Reproduces by seed and creeping roots.

Control Strategies:

In Fremont County, Perennial Sowthistle is seldom an economically important weed. It grows on wet saline pastures where grazing pressure selects for it over the grasses. The best control, twice over grazing, competitive grasses,   and moderate amounts of 2,4-D Low-Vol Ester spring and fall where the weed is dominating the site.  Curtail, Redeem, and Transline are also registered for use and will likely deliver good results.

To learn about biological control agents for Perennial Sowthistle visit this link.