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The yellow star thistle has a bushy appearance; stems are grayish-green in color and can grown 3’ to 5’ in height.  Leaves are covered with hairs that look thick and wooly.  The leaves that occur at the base are up to 3” long and have deep lobes; the leaves that occur on the upper portion of the stalk are short and narrow, giving the stem a “winged” appearance.

This plant produces bright yellow flowers that are surrounded at their base by sharp spines that are up to 3/4” in length.  Yellow star thistles reproduces only through seeds.   Each plant can produce up to 75,000 seeds  in a single growing season.   Seeds typically germinate after about a year, but can remain viable in the soil up to 10 years.

Yellow star thistle has a taproot that can grow to depths of 3 feet.  This long taproot provides the plant with the capacity to survive in hot, dry climates. Habitats are disturbed areas, roadsides, rangelands, waste areas, overgrazed lands, pastures, hay fields, along waterways, roadsides and forests.

If ingested by horses, yellow star thistle causes “chewing disease”; a neurological  disorder that creates brain lesions and ulcers in the mouth that can be fatal.

Biological Control of  Yellow Star Thistle

  • Yellow Star Thistle Hairy Weevil (Eustenopus villosus)

These hairy weevils feast on the star thistle flowers, helping to reduce the amount of seeds each plant produces.

Integrated Weed Management (IWM)

  • Mechanical applications such as hand pulling, hoeing, or mowing should be done before the plant produces viable seeds.  Flowerheads develop in early summer until a killing frost.  On average, seedheads  required about 21 days to progress from the pre-bloom stage to petal termination.
  • Fire management: Consult local authorities for assistance
  • Herbicides: Consult local Weed Board and/or Extension Agent for assistance

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