Purple Starthistle

Information

Centaurea calcitrapa - Asteraceae Family

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Identification

Flowers: The flowers are purple and 0.6 to 1 inches in diameter. Twenty-five to 40 florets (small flowers) make up each flower head. Underneath the flower are spine-tipped bracts that are greenish or straw-colored.
Seeds: The seeds are oblong and 2.5-3.5 mm long. They are white and often streaked with brown.
Leaves: The leaves are alternate, with deeply divided lower leaves and narrow and undivided upper leaves. The leaves are five to eight inches long and have dots of resin on their surfaces.
Flowering Time: The plant produces long stems in spring and early summer. It flowers from June through November.
Life cycle: Purple Starthistle can live as an annual in extremely favorable conditions, but most often lives as a biennial.

Impacts

Purple Starthistle can quickly displace native flora in disturbed areas due to its rapid growth and seed production.
Purple Starthistle is unpalatable to grazing animals and rapidly degrades the forage quality in any infested areas.
With thicker and stronger spines than its relatives, Purple Starthistle poses a threat of injury to both humans and animals moving through infested areas.

Most effective control methods

Small infestations of Purple Starthistle can be effectively controlled by manually pulling and disposing of plant remains. Plants should be cut at least 2 inches below the surface.
There are no effective biocontrol agents currently approved for use in the US to control Purple Starthistle.
Chemical control can prove effective on Purple Starthistle if applied in early spring. Multiple treatments may be needed for best control.

Purple starthistle: flower

Purple starthistle: rosette

Purple starthistle: flower and foliage

Purple starthistle: sharp spines

Purple starthistle: infestation

Purple starthistle

Purple starthistle: flowers, spines, and foliage