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  • Noxious Weed Identification List

    Musk Thistle

    (Carduus nutans)

    Fact Sheet Adobe PDF Icon 

    Colorado List B - Control required in Jefferson County


    • Family: Sunflower (Asteraceae)
    • Herbaceous
    • Biennial (short-lived perennial)
    • Rosettes formed the first year and bolt early in May to June of the next year



    • Pastures, rangeland, forests, disturbed areas, right-of-ways, ditch banks and grain fields from sea level to 8,000 feet
    • Grows in all soil textures, but soils must be well drained
    • Musk thistle out-competes desirable plants for resources




    • Mature plants grow up to 6 feet tall
    • Multi-branched
    • Leaves extend onto the stem, giving it a winged appearance
    • Bolts in late March through May
    • Leaves are hairless, dark green with light green mid-rib, deeply lobed; 1 to 1 1/2 inches wide and 4 to 5 inches long; yellow to white spine near tip



    • Tap root



    • Color: Purple
    • Season: May through August
    • Buds 1 inch or less wide; mature flowers are 1 1/2 to 3 inches wide
    • Droop from stem, giving it the name "nodding thistle"
    • Each head produces an average of 1,200 to 1,500 seeds 45 to 55 days after bolting
    • Seed is dispersed 7 to 10 days after flowering



    • Can germinate 6 to 8 weeks after falling to ground
    • May remain dormant in soil for more than 10 years
    • Dispersed by wind



    • Seedlings emerge in mid to late July
    • Rosettes can grow up to 4 feet in diameter
    • Spends winter as rosette



    • Seed




    • Rhinocyllus conicus, seed head weevil (may infest native thistles)




    • Prevention – maintain health of site
    • Removal – hand pulling before seed set; remove at least the top 2 to 4 inches of the root
    • Flowers must be bagged and disposed of



    • Burning - Fire has not been and effective control because it doesn’t get hot enough to kill the plant and its roots.  Burning may improve grass growth, encouraging competition 
    • Grazing - Ineffective because livestock only eat a few flowers.  Heavy grazing and associated disturbances near water, salt and loafing areas increase establishment of seedlings 
    • Mowing - Between the first appearance of pink on the earliest buds and brown on the pappus.  Plants may resprout


    Use all chemicals according to the manufacturer's label. Listing the above methods or products does not imply a specific recommendation or endorsement.

    Alicia Doran
    Weed & Pest Management Specialist





    Last Updated: 8-5-2013