Perennial Sowthistle

Corn sow thistle, creeping sow thistle, field milk thistle, field sow thistle, and hare’s lettuce

Perennial sowthistle seed germinates when the soil has warmed up in the spring. The seeds are reddish brown, ridged and wrinkled with a tuft of fine white hairs. When the plant is broken, both the leaves and stem exude milky latex. All the plant parts are filled with a bitter, milky juice. The seedling grows slowly for about 2 weeks until the leaves are about 1 inch long and then it forms a rosette. The first year the rosettes form vertical roots up to 6.5 feet deep. The root system is extensive and composed of downward and horizontally growing roots that can be 5- 10 feet deep that can produce new plants from small root pieces. Root pieces that have been cut during cultivation can produce a flowering plant within a year. Bolting usually occurs in the second year when the rosette has 12-15 leaves. Alternate, lower leaves are deeply lobed, upper leaves clasp the stem; similar to a dandelion leaf except with teeth ending in small weak prickles. Flowers are bright yellow up to 2 inches wide daisies and bloom from June through August. Perennial sowthistle spreads vegetatively, as well as through wind-borne seeds. A single plant can produce up to 9,750 seeds. 

The deep yellow flowers look similar to dandelions. Below the flower heads, the stem will have yellow hairs. Leaves clasp the stem and alternate with spiny toothed margins. 

Perennial sowthistle like to be in croplands, meadows, right-of-ways, rangeland, edges of gardens, and ditch banks. 

There are herbicides and other control methods that commonly control perennial sowthistle. Dicamba, 2,4-D, Triclopyr, and Milestone provide some control. Hand-pulling by the roots may provide some control.  For more information on these herbicides and other control methods contact the Crook County Weed and Pest office.  

 Perennial sowthistle is said to be a favorite for rabbits. In dry conditions is not favorable for Perennial sowthistle and is less of a problem in the dry years. Alfalfa and perennial grasses are strong competition for this plant.