Annual Sow Thistle
(Sonchus oleraceus)
Annual Broadleaves
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.
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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