Bull Thistle (Cirsium vulgare)

Click on the photo to enlarge (Photo maybe used for non-profit uses with attribution to Mesa County Division of Pest Management).

County Management Strategy: Contain infestations above approximately 7,000 feet elevation. Eradicate infestations below approximately 7,000 feet elevation.

Identification: A tap rooted, biennial, spiny leaved thistle with large dark purple flowers clustered at the ends of branches. First year growth is a low growing rosette of leaves. In the second year it blooms from June through the summer. The vase shaped flowerheads are 1½"-2" in diameter. Bull thistle grows 2-5 feet tall and has very green leaves with pointed lobes. Leaves have a cottony underside.

Other names: Common thistle, spear thistle

Similar Species: The rosette of musk thistle is similar but not as green as bull thistle. Flowers of other thistles are not vase shaped, but more open and less compact. Cirsium traceyi (formerly C. undulatum and commonly called wavy leaf thistle), a native thistle often confused with bull thistle, has paler purple flowers and silver gray leaves. Control Timing: Control plants before they bolt, in the spring. Rosettes should be killed manually or with herbicides in the spring or fall. Plants that are bolting should be removed manually or sprayed as soon as possible. Flowering plants should be removed manually and mature flowerheads bagged to prevent seed spread.

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.

Status in Mesa County: Scattered and occasional; in pastures, waterways, and disturbed sites. County Management Strategy: Contain infestations above approximately 7,000 feet elevation. Eradicate infestations below approximately 7,000 feet elevation.

Identification: A tap rooted, biennial, spiny leaved thistle with large dark purple flowers clustered at the ends of branches. First year growth is a low growing rosette of leaves. In the second year it blooms from June through the summer. The vase shaped flowerheads are 1½"-2"

Photos:
http://www.invasive.org/species/subject.cfm?sub=3393

Fact sheets and control:
http://www.colorado.gov/cs/Satellite?c=Page&cid=1178305507366&pagename=Agriculture-Main%2FCDAGLayout

Additional links:
http://http://www.cnr.uidaho.edu/rx-grazing/Forbs/Bull_Thistle.htm