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  • Noxious Weed Identification List

    Scotch Thistle


    Onopordum acanthium

    Fact Sheet Adobe PDF Icon

    Colorado List B - Control required in Jefferson County

    General

    • Family: Sunflower (Asteraceae)
    • Biennial
    • Native to Europe and eastern Asia

     

    Habitat

    • Found in rangelands, disturbed areas and right-of-ways
    • Thrives in moist areas

     

    PLANT

    Vegetation

    • Mature plants are 12 feet tall
    • Leaves are up to 2 feet long and 1 foot wide
    • Covered with dense hair
    • Stems have spiny wings

     

    Roots

    • Tap root

     

    Flower

    • Color: violet
    • Season: mid-June through September
    • Size: 1 to 2 inches wide
    • Spiny bracts

     

    Seed

    • One plant can produce 20,000 to 40,000 seeds
    • Seeds germinate in the fall and spring
    • May remain viable in soil for more than 30 years

     

    Seedling

    • Rosettes can grow 6 feet wide
    • Forms dense patches
    • Rosettes form the first year and bolt early May to June of the next season

     

    Reproduction

    • Seed

     

    CONTROL

    Biological

    • None

     

    Chemical

    Apply one of the following during the rosette stage (spring or fall):

    • Banvel; or
    • Curtail; or
    • Transline; or
    • 2,4-D; or
    • RoundUp (spot treat); or
    • Tordon (restricted-use pesticide)

     

    Apply one of the following during the early bolt stage (spring through early summer):

    • Banvel; or
    • Curtail; or
    • Transline; or
    • RoundUp (spot treat); or
    • Tordon (restricted-use pesticide)

     

     

    Cultural

    • Prevention – maintain health of site using good grazing management and keeping good cover
    • Removal
    • Revegetation of highly disturbed sites

     

    Mechanical

    • Burning - May cause seeds to germinate 
    • Grazing - N/A 
    • Mowing - When used with other methods 

     

    More Information

     

    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-scotch-thistle-plant


    Last Updated: 7-30-2013