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  • Noxious Weed Identification List

    Spotted Knapweed


     

    Centaurea maculosa aka C.stoebe, C. biebersteinii

    Info Sheet Adobe PDF Icon

    Colorado List B - Eradication required in Jefferson County

    General

    • Family: Sunflower (Asteraceae)
    • Native Range: Central Europe
    • Introduced to North America in the late 1800s or early 1900s
    • Very invasive herbaceous, long-lived biennial (short-lived perennial)

     

    Habitat

    • Found in meadows, pastures, roadsides and sandy or gravelly sites
    • Soil erosion is sometimes a problem because roots don’t hold soil as well as native vegetation
    • Causes serious decline in forage and crop production
    • Heavily infested areas will probably need to be reseeded once the plant is controlled

     

    PLANT

    Vegetation

    • Plant is 1 to 4 feet tall
    • Forms rosettes the first year and bolts in the spring of the second growing season (May to June)
    • Rosette leaves are 6 inches long and deeply lobed
    • 1 to 20 upright stems, 1 to 3 feet long

     

    Roots

    • Tap root

     

    Flower

    • Color: pink or purple
    • Single 3⁄4 to 1 inch wide
    • Bracts have black tips, fringed edges; no terminal spine
    • Flowering occurs summer through fall (late June to October)

     

    Seed

    • Each plant can produce as many as 40,000 seeds
    • Most seeds fall within 3 feet of the plant
    • Seeds can stay dormant for 8 years

     

    Seedling

    • Seeds germinate in spring or fall

     

    Reproduction

    • Seed

     

    CONTROL

    Biological

    • None; biological control is not an option under eradication

     

    Chemical

    Apply during rosette to early bolt stage (spring); rosette (fall):

    • Aminopyralid (Milestone) 

     

    Apply one of the following after all shoots have emerged, rosette to early bud (spring); rosette (fall):

    • Clopyralid (Transline, Stinger)
    • Clopyralid plus 2,4-D (Curtail)  

     

    Apply during rosette to mid-bolt stage (spring); rosette (fall):

    • Picloram (Tordon 22K – restricted-use pesticide)

     

    Apply during rosette stage (spring and fall):

      • Dicamba (Banvel, Vanquish or Clarity)

    Cultural

    • Prevention – maintain health of site
    • Removal - make sure entire root is removed; must be repeated as new plants germinate; any flowers must be bagged and disposed of at a landfill
    • Revegetation - maintaining good ground cover helps prevent reinfestation

     

    Mechanical

    • Burning - N/A 
    • Grazing - N/A 
    • Mowing  - Mow before flowering, followed with herbicide treatment 

     

    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

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    Last Updated: 7-31-2013