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Plumeless Thistle
(Carduus acanthoides)
County Management Strategy: Eradication throughout the County.
Identification: An annual, highly branched, tap rooted biennial thistle growing up to 4 feet tall. Rosette leaves are 4 to 8 inches long, green, with spined lobes. Stem leaves have “wings” that grow to the stems. Flower stems also winged. The purple flowers are either solitary or in a cluster of 2-5. Flowers rarely white or yellowish. Bracts under the petals are hairy and narrow.
Other names: spiny plumeless thistle
Similar Species: Musk thistle has larger bracts and flowers, and the flower stems are not winged. Bull thistle is shorter and not as spiny with more compact flowers. Flowers of the rare native species, Cirsium perplexans, are borne singly rather than in clusters and the stems are not profusely winged. Cirsium traceyi (formerly C. undulatum and called wavy leaf thistle), another native thistle, is not very branched, has silver gray leaves and the stems are not winged.
Control Timing: In the rosette and early bolting stages.
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. However, biological control is not recommended in Mesa County because eradication is the management goal for this species.
Status in Mesa County: Infestations have been found in Devil’s Canyon near Fruita, in the Brush Creek area east of Collbran and in Rifle (Garfield County). Otherwise it is not widespread in Mesa County. REPORT INFESTATIONS TO THE DIVISION OF PEST MANAGEMENT!
Photos:
http://www.ppws.vt.edu/scott/weed_id/cruac.htm
Fact sheets and control:
http://www.botany.wisc.edu/wisflora/scripts/detail.asp?SpCode=CARACA
http://www.co.douglas.ne.us/dept/envserv/plume.htm
Additional Links:
http://www.invasive.org/browse/subject.cfm?sub=3400
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