Musk Thistle (Carduus nutans)

County Management Strategy: Contain infestations above approximately 7,000 feet elevation. Eradicate infestations below approximately 7,000 feet elevation. Identification: A bushy biennial plant that grows to 6 feet tall. The dark green leaves have spines along the edges and are lobed and wavy. Rosette leaves are spiny with a white central vein that is very visible on the underside. Leaves often have a whitish edge. The leaves clasp the stem and form “wings” along the stem below the leaf. Flowers are borne singly on long spineless stems. The flowers are deep pink to magenta and 1½ to 3 inches in diameter with very broad green or somewhat magenta bracts below the petals. When mature, the flowers “nod,” hence the other common name, nodding thistle.

Other names: nodding thistle, plumeless thistle, nodding plumeless thistle Similar Species: Plumeless thistle, another noxious species, has spined “wings” along the stem below the flowerhead and the flowers may occur in clusters of 2-5 flowers. Bull thistle, another noxious species, is shorter and the lobes of the leaves are sharply pointed and at right angles to the main vein. None of our native thistles are similar to musk thistle.

Control Timing: In the rosette (spring and fall) and early bolting stage.

Control target: Prevent seed production.

Control Methods: Severing the tap root at least 2" below the soil line before flowering is very effective. Herbicides can be used in the rosette to early bolting stage. Flowering plants should be chopped and bagged to prevent spread of seeds. Several insect species are available for biological control.

Status in Mesa County: Widespread in higher elevations of Mesa County in disturbed areas, on roadsides and in pastures. Occasionally found in lower elevations in Mesa County.

Photos:
http://www.psu.missouri.edu/fishel/musk_thistle.htm

Fact sheets and control:
http://www.nps.gov/plants/alien/fact/canu1.htm
http://www.ext.colostate.edu/pubs/natres/03102.html