Noxious Weeds Profile - Sowthistle, annual, perennial

Table of Contents


  • English - annual sowthistle, perennial sowthistle
  • French - laiteron lisse, laiteron des champs
  • Latin Name - Sonchus oleraceus L., Sonchus arvensis L.


Annual sowthistle.

Figure 1. Annual sowthistle

Perennial sowthistle.

Figure 2. Perennial sowthistle

Current Status

  • Ontario Weeds Act - noxious
  • Other provinces - noxious in AB, BC, MN, QC, SK (perennial); AB, BC, MN, QC, SK (annual)
  • Canadian Federal Seeds Act - perennial Class 2 & 5
  • U.S. Federal Noxious Weed - no
  • U.S. Noxious State Reg - perennial 18 states (including Illinois, Indiana, Mich, Ohio, Penn); annual none


  • Pub 505 - no
  • NE Weeds - no
  • Canadian Poison Plant - not listed
  • Cornell Poison Plant - not listed


  • Throughout Ontario in cultivated fields, pastures, meadows.

Growth Habit

  • Annual and Perennial

Method of Propagation

  • Seeds (Wind blown)


  • Annual - Susceptible to 2,4-D and dicamba and listed on 2,4-D and Roundup labels. A single mowing before flowering can give effective control.
  • Perennial - Susceptible to dicamba and glyphosate and top growth control only with 2,4-D. Listed on 2,4-D, Banvel and Roundup labels. Apply herbicide at early bud (flowers mid summer) or in early fall. Repeated mowing at 21 day intervals can be an effective control.

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