Squarrose knapweed (Centaurea virgata var. squarrosa)



  • Squarrose Knapweed Plant 215x150

Category A Weed

Sunflower family (Asteraceae)

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Stem

  • Up to 2 ft. tall, highly branched and rough-textured; multiple stems can arise from woody crown; NO wings on upper stems

    Leaves

    • Exist as a basal rosette prior to bolting; alternate; lower leaves pinnate-divided and 4-8 in. long; sometimes covered with short grayish hairs; upper leaves strap-like (linear) with smooth edges (margins)

      Flower

      • Pink to purple, each located at the tip of a branch; base of flower is narrow vase-shaped, 0.3 in. long, 0.12 in. wide and covered with comb-like bracts, tipped with a spine (less than 0.12 in. long) that curves outward

        Root

        • Deep, stout taproot

          Other

          • Often infests rangelands, waste areas and roadsides; known to occur in Elko and White Pine counties

          • Perennial; reproduces by seed

            Control

            • Mowing plants in bud to flower stage can reduce seed production; repeated hand removal can be effective; DO NOT burn

            • Several insect biological control agents are available

            • Apply 2,4-D or dicamba in the rosette stage; clopyralid, picloram or aminopyralid between rosette and mid-bolt stages

              Images

              Squarrose Knapweed Plant 215x150
              Mature plant
              Squarrose Knapweed Seedling 215x150
              Seedling
              Squarrose Knapweed Rosette 215x150
              Rosette
              Squarrose Knapweed Flower 215x150
              Flower
              Squarrose Knapweed Leaves Stem 215x150
              Leaves
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