Perennial Sowthistle

Perennial Sowthistle is also known as:
  • Creeping sow-thistle
  • Field milk thistle
  • Field sow-thistle
  • Cultivated fields
  • Meadows
  • Roadsides
Perennial Sowthistle is a creeping perennial with an extensive horizontal root system. It is reproduced by seeds and underground roots. The roots penetrate to a depth of 1.5 - 3 meters. The stem, which can grow up to 1.2 meters, is hollow, smooth and branches at the top. The plant also contains a milky substance inside the stem. The leaves alternate with a slightly toothed edge. Lower leaves have deep cut, backward pointing lobes. Leaves are approximately 15 - 30 cm long with upper leaves being smaller. The flowers are yellow in color; almost like a dandelion. They are 1.3 - 5 cm across. Seeds are small, brown, ridged and crowned with a tuft of fine hairs.

Control Practices
Tillage is the most effective way to control Perennial Sowthistle because it starves the root system. Start tillage as soon as possible after harvest, preferably with a cultivator. The next spring one of the following should be completed:
  • Start tillage early in spring and continue until freeze-up. Green growth should not remain above ground for more than a week.
  • Start tillage when the buds are in their early stage as this is when the plant is the weakest. Continue tillage until freeze-up.
  • Summerfallow until mid July to control other weeds. Then leave the Perennial Sowthistle undisturbed. When it reaches the early bud stage it should be sprayed with the appropriate chemical.