Perennial Sow Thistle
Sonchus arvensis L.
Family:
Asteraceae
Description and life cycle
Perennial sow-thistle is a herbaceous perennial that
reproduces from seed and from an extensive creeping root system. The
roots penetrate down to 3 m, but, most of the system is within the
top 5 – 15 cm of soil. Roots break easily and regenerate from buds.
Hollow, erect stems can reach 0.6 – 1.5 m tall and contain a bitter,
milky juice. Stems are non-branching until near the top. A variety
of leaf shapes and sizes are arranged alternately along the stem –
upper leaves are clasping while the lower leaves narrow to a winged
stalk. All leaves have deep lobes and weak prickles along their
margins. Bright yellow blossoms appear in June and continue into
September. At peak bloom, each flower can reach 3.8 cm across. A
single plant can have as many as 20 flower heads, but, few come into
flower at the same time. It is a prolific seed producer with about
10,000 seeds produced per flowering stem. The ribbed seeds have
attached pappus which assists with their distribution.
Biological control agents
References
British Columbia Ministry of Agriculture and Food. No date. Perennial sow thistle (Sonchus arvensis L.). agdex 640. Govt. of BC.
Cranston, R., D. Ralph and B. Wikeem. 2005. Field guide to noxious and other selected weeds of British Columbia. Gov. of BC. 94 p.
Frankton, C. and G. A. Mulligan. 1987. Weeds of Canada.
Parish, R., R. Coupe and D. Lloyd. 1996. Plants of southern interior British Columbia.
Peschken, D. P. 1982. Host specificity and biology of Cystiphora sonchi [Dip: Cecidomyiidae], a candidate for the biological control of Sonchus species. Entomophaga, 27: (4): 405-416.
Whitson, T. D. (editor), L. C. Burrill, St. A. Dewey, D. W. Cudney, B. E. Nelson,
R. D. Lee and R. Parker. 1992. Weeds of the west. Western Soc. Weed Sci. and Western U. S. Land Grant Univer., Cooperative Extension Serv.
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