Yellow Starthistle
Centaurea solstitialis
Washington State Classification
Class B — Control Required (Designated)
It is an aggressive species that has invaded millions of acres of rangelands in the western United States.
Required control in Region 1 (all western Washington counties)
Quick Reference
Identification
Growth Habit
Yellow starthistle is an annual or biennial growing 20 to 80 cm tall (18 to 36 inches). Plants have deep taproots, winged stems and are covered in thin white, woolly hairs.
Leaves
Basal leaves lobed, sometimes with the terminal lobe larger and more rounded than the other lobes. Stem leaves smaller, becoming narrower and not lobed.
Flowers
Flowerheads with a wide base and composed of yellow flowers. Bracts at the base of flowerheads with spine tips of varying lengths. Larger spines on bract tips are 3/8 to 3/4 inch long (1.1 to 2.2 cm), yellowish in color and are star-like in arrangement.
Fruit & Seeds
There are two types of seeds, both are 2 to 3 mm long and hairless. Outer seeds are dark brown and are without bristles (pappus). Inner seeds of seed head are glossy, white or light brown and mottled with short, white bristles (pappus) on one end.
Impact
It is an aggressive species that has invaded millions of acres of rangelands in the western United States. Cattle feeding on it may be poorly nourished and can be damaged by the spiny heads. Horses may be poisoned and develop chewing disease.
Ecology & Spread
Habitat
Yellow starthistle is found in rangeland, edges of cropland, abandoned farmlands and pastures as well as along roadsides, railways and recreational areas. Please click here to see a county level distribution map of yellow starthistle in Washington.
Spread Mechanisms
Reproduction
Yellow starthistle reproduces by seed.
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Control Methods
Mechanical
- Mechanical removal is not economically feasible for large, dense infestations. Small infestations may be hand-pulled, tilled or mowed. Areas should be monitored and controlled frequently during the growing season.
Biological Control
- There are a number of biological agents used on yellow starthistle. The yellow starthistle hairy weevil, Eustenopus villosus, larvae and adults interfer with the seed production of yellow starthistle. The adults feed on young seedheads and the larvae feed inside flowerheads. The yellow starthistle flower weevil, Larinus curtus, larvae feed on developing yellow starthistle seedheads. The yellow starthistle bud weevil, Bangasternus orientalis, larvae feed within seedheads and reduce seed production. The yellow starthistle peacock fly, Chaetorellia australis, larvae feed within seedheads. The yellow starthistle rust, Puccinia jaceae var. solstitialis, is a fungus that attacks yellow starthistle. The yellow starthistle gall fly, Urophora sirunaseva, larvae are associated with galls formed within seedheads. For more information about these biological control agents of yellow starthisle, please visit WSU Extension Integrated Weed Control Project.