Perennial Sowthistle

perrenial sowthistle

Sonchus arvensis • Class C

Family Name: Asteraceae (ass-ter-AR-see-ee)
Common: Field sowthistle, Creeping sowthistle
Genus: Sonchus (SON-chus)
Meaning: From the Greed sonchos, meaning hollow in reference to the stem
Species: Arvensis (Ar-VEN-sis)
Meaning: Of farmed or cultivated land

Despite the name, Perennial sowthistle resembles dandelions more than it does true thistles. Perennial sowthistle usually grows 2 to 4 feet high and has an extensive root system that grows up to 10 feet deep and can spread more than 6 feet in one growing season. It has erect, hollow stems with bitter, milky juice. Its leaves vary in size and are alternate, prickly edged, and lance shaped. Flower heads are 1 to 2 inches across and bright yellow. Its bracts are green with white margins and covered with tiny hairs. 

 Why Is it a Noxious Plant?

P.S. is an aggressive spreader, a single plant can produce 4,000 to 13,000 seeds that can remain dormant in the soil for up to 6 years. It can be hard to get rid of, because even small pieces of the extensive root system can regenerate new plants. 

Where Does it Grow?

Perennial sowthistle is found cultivated fields, waste areas, meadows, sloughs, woods, lawns, roadsides, beaches, ditches and river and lake shores. 


Perennial sowthistle can form dense monocultures by the spread of its rhizome-like roots. At high densities perennial sowthistle can drastically reduce water resources and likely decreases native plant diversity and is a problem in several crops, where it causes economic losses due to reduced crop yields increased expenses, and land depreciation. It is also a host of several economically damaging plant pests. 

Control Options:

As with all invasive species, the best control measure for Perennial sowthistle is prevention. Preventing the establishment of infestations is the most time and cost effective way of controlling this species. Above all, prevent plants from going to seed. 

  • Both cattle and sheep can pasture on infested land and are considered an effective control method. 

  • Replanting areas where control work has been done is critical to reducing Perennial Sowthistle numbers in future seasons. Sowthistle rarely thrives where competing species are well established and maintained. 

  • Small isolated plants can be effectively controlled by hand pulling and digging out as much of the roots and rhizomes as possible. 

  • This plant is relatively resistant to many, but not all, common broadleaf herbicides. Spot spraying with an herbicide containing the active ingredient glyphosate (Roundup Pro, Glyfos, etc.) may be used effectively in the spring while the plant is actively growing, up to when the flowering stem bolts. The goal is to insure all plants have emerged. Cut the plant tops off before an herbicide application to prevent seed production, and spray each plant thoroughly on the stems and leaves, enough to be wet but not dripping. Be aware, glyphosate is non-selective and will injure any plants that it comes in contact with, including grass. 
  • For selective control of sowthistle in agricultural settings (pastures, hayfields, etc.): an herbicide containing the active ingredient aminopyralid (example: Milestone, Milestone VM, etc.) may be applied in the spring while plants are actively growing, it is also effective in the fall before a killing frost. Aminopyralid products will not harm grass and can be used around livestock (provided all label precautions are followed). 
  • Currently, no biocontrols are available in Washington. 
  • When using herbicides, always read and follow all label instructions and obey all label precautions. (Note: pesticide product registration is renewed annually and product names and formulations may vary from year to year.)  

More Information:

 Download our Flyer or visit Washington State Noxious Weed Control Board Here. Photo by Leo Michels


More Pictures:  

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