Yellow Startthistle


  • Whitish hairs on leaves; upper leaves appear winged
  • Sharp spines below yellow flower head up to 1 inch long
  • Yellow flowers similar to spotted knapweed flowers
  • Height 3 to 5 feet

Video Information

Weed Pictures

Weed Information

ToxicityToxic. Horses.
ControlBiological, hand pulling/digging, herbicide and mowing. Contact your County Weed District or local Applicator for more information.
HabitatGrassland, rangeland, pastures, cultivated fields, disturbed sites and roadsides.
RootLarge taproot that grows to soil depths of 3 to 5 feet.
Leaf ShapeDeeply lobed rosette, linear mature leaves.
LifespanWinter annual; one year life cycle; may germinate in fall or spring.
Priority 1A WeedNot present or limited presence in Montana. If you think you’ve found this plant, please contact your county weed coordinator or Montana Department of Agriculture immediately!
Similar Looking PlantsAt rosette stage, other knapweeds.
Important InformationYellow starthistle spreads primarily by seed dispersal and seeds remain viable in the soil for up to 10 years. It causes chewing disease in horses and has been known to puncture car tires.