header background image
Current Weather 37° F
  • Jefferson County Parks Banner
  • Noxious Weed Identification List

    Musk Thistle


    (Carduus nutans)

    Fact Sheet Adobe PDF Icon 

    Colorado List B - Control required in Jefferson County

    General

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

     

    Habitat

    • 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

     

    PLANT

    Vegetation

    • 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

     

    Roots

    • Tap root

     

    Flower

    • 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

     

    Seed

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

     

    Seedling

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

     

    Reproduction

    • Seed

     

    CONTROL

    Biological

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

     

    Chemical

    Cultural

    • 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

     

    Mechanical

    • 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
    303-271-5989
    adoran@jeffco.us

    weed-pest-b-musk-thistle-flower3

    weed-pest-b-musk-thistle-flower4

    weed-pest-b-musk-thistle-leaves

    weed-pest-b-musk-thistle-habit


    Last Updated: 8-5-2013