Milk Thistle

Silybum marianum

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Milk Thistle - A large, sparsely branched thistle growing up to 6 feet tall. Easy to identify, due to the leaf patterning.

Leaves: Alternate, deeply lobed, and pointed leaves. Leaves have a very noticeable white and dark green marbling. The basal leaves can get up to 20 inches long and 10 inches wide.

Flowers: Flowers bloom from May-August. Rounded cluster of tubular flowers that have spine-tipped bracts (scales) around it.

Habitat: Occurs in many places such as: overgrazed pastures, roadsides, waste areas, ditches, and disturbed areas.

Weed Classification: A

Why is it a Noxious Weed?

It is an aggressive invader that can grow into dense stands. Being a nitrate accumulator, it can poison livestock if they graze the plant.

Milk Thistle has been found in Lewis County, and can produce many seeds that allow it to spread. If you think you see Milk Thistle please let us know!

Control Recommendations:

WA State Noxious Weed Control Board

PNW Pest Management Handbook

UC Davis Weed Report