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  • Noxious Weed Identification List

    Hoary Cress


    (Cardaria spp)

    Colorado List B - Control required in Jefferson County

    Info Sheet Adobe PDF Icon 

    General

    • Family: Mustard (Brassicaceae)
    • Found in moist and transitional areas along right-of-ways, fields and cropland
    • Introduced in late 19th century from Europe

     

    Common names

    • Whitetop

     

    Habitat

    • Alkaline and disturbed soils
    • Very competitive once established
    • Easily displaces native vegetation
    • Forms monoculture
    • Creeping perennial
    • Mature plants grow up to 2 feet tall

     

    PLANT

    Vegetation

    • Leaves are blue-green
    • Lower leaves are stalked
    • Upper leaves have two lobes that clasp the stem
    • Oval or oblong with toothed or almost smooth margins
    • Leaves are often covered with very fine, white hairs

     

    Roots

    • Deep-rooted, creeping perennial
    • Rhizomatous lateral roots send up shoots that develop independent taproots
    • Hoary cress roots release chemicals that hinder growth of cereals

     

    Flower

    • Color: typically white, four petals
    • Season: late April and May
    • Size: 1/8 inch across
    • Multiple flowers clustered at the end of stems.

     

    Seed

    • Mature plant produces 1,200 to 4,800 seeds
    • Seeds are viable for 1 to 2 years
    • Heart-shaped seed pod contains two oval, finely pitted, red-brown seeds each about 1/2 inch long

     

    Seedling

    • Most emerge in April, some fall germination possible under optimum conditions.

     

    Reproduction

    • Seed and vegetative means

     

    CONTROL

    Biological

    • None

     

    Chemical

     

    Cultural

    • Prevention – Maintain health of site
    • Hand pulling - Is only minimally effective because the plants regenerate from the roots
    • Cultivation  - Spreads the plant and is not recommended unless the area is plowed every couple weeks during the growing season for up to three years

     

    Mechanical

    • Burning - Not effective
    • Grazing - Not recommended; not readily grazed by livestock. May poison livestock; may taint meat and milk
    • Mowing - Not recommended; may spread seed. May disturb root system; new plants form off of the plant fragments

     

     



    Alicia Doran
    Weed & Pest Management Specialist
    303-271-5989
    adoran@jeffco.us

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    Last Updated: 8-5-2013