WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Annual Sow Thistle

(Sonchus oleraceus)

Annual Broadleaves

 

Annual Sow Thistle

 

Habitat Characteristics

Common weed of landscapes, nursery crops, orchards, grain fields, cultivated crops, and waste areas.

 

Identification

This annual weed can grow up to 4 feet tall with smooth, erect stems. The leaves on elongated stems are alternate and smooth and vary in shape from deeply lobed to triangular. Leaf margins are slightly prickly. The pale yellow ray flower heads, ¼ inch to ¾ inch in diameter, are in clusters at the ends of the stems. The seed is long, wrinkled and brown, with feathery hairs to aid in dispersal. The taproot is short.

Annual Sow Thistle

Annual Sow Thistle

Annual Sow Thistle

Life History

Reproduction is by wind-blown seed. Seeds germinate in mid to late spring but continue to emerge throughout the season in moist, cold sites. Flowers are produced from July to October. After frost, plants turn dark brown to black and persist for only a short time.

 

Management

Cultural Techniques

     - Seeds germinate in the top ½ inch of soil, so frequent cultivations can control this weed.

Chemical Techniques

     - See Herbicide Efficacy Table (pdf)

 

Web References

University of California IPM, Weed Gallery, Annual Sowthistle http://www.ipm.ucdavis.edu/PMG/WEEDS/annual_sowthistle.html

USDA – NRCS Plant Profile, Annual Sowthistle
http://plants.usda.gov/java/profile?symbol=SOOL

Weeds B.C., Annual Sow Thistle
http://www.weedsbc.ca/weed_desc/ann_sow.html

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WSU Whatcom County Extension • 1000 N. Forest St., Bellingham, WA 98225 • (360) 778-5800 • whatcom@wsu.edu