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Pest Information

Blessed Milk-thistle

Blessed Milk-thistle

  • Latin Name: Silybum Marianum
  • Common Name: Blessed Milk-thistle
  • Other Names: Milk thistle, white thistle, bull thistle

Pest Details

Blessed Milk-thistle
Blessed Milk-thistle
Blessed Milk-thistle


Native to the Mediterranean region, and naturalized in the western United States.


A winter annual or sometimes a biennial weed. Seedlings germinate in the fall, and by mid-winter substantial foliage is present.


Mature plants have foliage that may grow up to 3 feet high in a broad, spreading manner, and flower heads may rise to over 6 feet high. Plants are easily recognized by the huge, wide leaves that may be over 12 inches long and are have distinctly white veins against the dark green leaf color. The first leaves are largest and form a rosette at the base, with subsequent leaves forming along the stout stems and being smaller. Leaves are clasping at the stem and have margins that are very spiny and deeply lobed and wavy. Flower heads occur singly at the ends of long stems, although main stems may branch along the way up, leading to several flowering stems arising from a major one. The flower head is very large and somewhat spherical, with spiny bracts surrounding it. The petals are purple.

Characteristicts Important to Control:

Seed dispersal can be very widespread due to the wind-blown seeds. Hand removal is appropriate and plants do not tolerate winter tilling.

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