Weed of the Week

July 5th 2006

Diffuse Knapweed, Centaurea diffusa Lam.

                   

 

Characteristics

Family: Asteraceae (Sunflower)

Origin: Came to the US from Eurasia

Description:

• Biennial
• Forms a rosette in the first season of growth
• Bolts, flowers, and sets seed in the second year of growth
• Reproduces only by seed

Stems:

• Single stemmed, multi-branched, erect and rough
• Grows up to 1-2 feet tall
• The base of the stem weakens toward fall.  Strong winds break the plant loose which them tumbles across the landscape scattering seeds as it goes

Flowers:

• White, sometimes pink colored flowers, bracts have numerous spines.
• Flowers are abundant and narrow
• Bloom occurs June-September
• Seeds are brownish or gray

Leaves:

• Leaves of rosettes are divided into narrow sections
• After bolting, leaves are pinnate, and become reduced in size

Location:

    Diffuse knapweed is a very common range, pasture and roadside weed along the Front Range.  Tumbleweeds can build up along fence lines, where seed accumulates.  It rapidly becomes established requiring years of monitoring and control.

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