Family: Asteraceae (Sunflower).
Other Common Names: St. Barnaby’s thistle, yellow cockspur.
Growth Form/Reproduction: Winter annual. Seed.
Legal Status Central Kootenay: Weed Control Act, Forest and Range Practices Act, Community Charters Act.
Agricultural: Infestations can reduce forage quality and forage availability in pastures and in hay. Prolonged grazing by horses can result in a fatal nervous disorder.
Ecological: Competes with native grass species.
Human: Dense stands impede recreational access.
Habitat: Shade intolerant. Adapted to soils ranging from deep and loamy to well-drained shallow and rocky soils on sites where annual precipitation varies from 25 – 100 cm. Disturbed sites, grasslands, pastures, hayfields, roadsides, recreational areas, and cropland.
Status and Distribution: Not known to occur in BC.
Management Strategy: Good pasture management can prevent or limit new infestations of yellow starthistle. Small infestations can be controlled by hand-pulling. Herbicides, such as 2,4-D, provide good control at the seedling or rosette stage but are not effective once the plants begin flowering. Five biocontrol agents have been released in the western US but none are present in Canada.