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Pest Information

Annual Sowthistle

Annual Sowthistle

  • Latin Name: Sonchus Oleraceus
  • Common Name: Annual Sowthistle
  • Other Names: Common sow-thistle, hares lettuce, colewort, milk thistle, sow-thistle

Pest Details

Annual Sowthistle
Annual Sowthistle
Annual Sowthistle


Native to Europe and found commonly throughout North America.


An annual weed found in virtually any crop or non-crop setting, and a common weed pest in landscaped habitats. It favors cool, moist environments and will die back in hot weather, but may continue to germinate seeds in cool landscapes. Propagation is from seeds, and these have long, silky hairs that enable the wind to disperse them great distances from the parent plant. Germination begins in mid-winter to spring.


Mature plants may grow to 6 feet tall, with 3 to 4 feet tall most common. Stems are wide, hollow, and usually with many branches. If the stems or leaves are broken or crushed they will ooze a sticky white juice. Leaves are fairly sparse along the stems, and are pointed and up to 9 inches long. The leaf margins are sharply toothed but not spiny, and may be deeply lobed. Leaves are clasping, surrounding the stem at the leaf base with a pair of lobes. Flowers are borne in clusters at the ends of the stems. They are pale yellow, and the many petals are in a ray arrangement. Outer, or lower, petals are much longer than the inner petals, giving the flower head a flat-topped appearance. As the seeds mature they produce a long, white, feathery pappus, giving the entire head a soft cotton ball appearance. Distinguished from Spiny sowthistle by the leaf margins not being prickly and by the short taproot.

Characteristicts Important to Control:

Seeds are dispersed widely by the wind. Physical removal is possible but should be done prior to seed maturation to avoid new seed dispersal.

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