Centaurea solstitialis L.
- St. Barnaby’s Thistle
- Golden Star Thistle
- Yellow Centaury
- Yellow Cockspur
- Maltese Star Thistle
General: Yellow Starthistle is a winter annual and occasional biennial in the Asteraceae (sunflower) family.
Flowers: Are yellow and singular at the end of branches. Flower heads are protected beneath by long (2 cm), sharp thorns in a star-like arrangement.
Stems: Mature plants are 60 – 90 cm tall. Dull green stems are rigid, branching, winged and hairy.
Leaves: Basal leaves are alternate and lobed with smooth margins, while stem leaves are entire and sharply pointed with wavy margins.
Seeds: Plumed (hairy) seeds are glossy and light brown with short, white bristles on one end. Plumeless seeds are smooth and dark brown. Both seeds measure 2- 3 mm long.
Roots: Yellow Starthistle rapidly develops deep, strong taproots.
Invasive: Spotted Knapweed (Centaurea stoebe) is found throughout the Sea to Sky region. Unlike Yellow Starthistle, Spotted Knapweed does not have winged stems. To add, Spotted Knapweed flowers are pink or purple.
Habitat and Origin
Yellow Starthistle is native to Europe, Asia, and Northern Africa. In the 1800s, it was introduced to North America through contaminated seed.
The species requires ample light, prefers dry environments, and can tolerate a range of soils. Consequently, it invades rangelands, pastures, roadsides, cropland and other disturbed habitats located at mid to high elevations.
Propagation & Vectors of Spread
Yellow Starthistle spreads through seeds, which may lay dormant in the soil for several years. Typically, plants produce 700 – 1,000 seeds, but vigorous plants are capable of producing up to 170,000 seeds.
Plumed (hairy) seeds are dispersed by wind and may “hitch” a ride on animals, humans, vehicles, and equipment. Plumeless seeds remain in the seed head until it disintegrates in the autumn or winter. Yellow Starthistle may also spread in contaminated seed mixes, grains and hay.
Ecological, Economic, & Health Impacts
- Possesses pioneering capabilities.
- Deters the growth of other plants around it (allopathic effect).
- Displaces native vegetation, thus reducing biodiversity.
- Poisonous to horses and harmful to grazing cattle.
- Dense infestations reduce forage availability and quality.
- Dense stands impede recreational access.
What Can I Do?
Yellow Starthistle is not currently found in communities in the Sea to Sky, so PREVENTION is key:
Learn to identify Yellow Starthistle: use the images presented on this profile page to learn how to identify Yellow Starthistle.
What to do if you spot it: You can report any Yellow Starthistle sighting by clicking here.
- Regularly monitor properties for weed infestations.
- Minimize soil disturbances and promptly revegetate disturbed areas to prevent the growth of Yellow Starthistle.
- Check wildflower mixes to ensure that they do not contain Yellow Starthistle.
- Ensure all flowering heads or buds are bagged or covered to prevent spread during transport to designated disposal sites.
- Unload, park or store equipment or vehicles in infested areas; remove plant material from any equipment, vehicles or clothing used in such areas and wash equipment and vehicles at designated cleaning sites before leaving infested areas.
- Plant Yellow Starthistle in a garden, no matter how well-contained its enclosure may seem.
- Compost any flowering heads or buds. Instead, dispose of Yellow Starthistle in the general/household waste stream at the landfill as the seeds will be able to persist in the composting process.
- Move soil, gravel, or fill that has been contaminated with Yellow Starthistle.
- Pulling, hoeing, and digging can remove small infestations, but these methods are ineffective with large populations.
- Mowing is also relatively ineffective as a long-term solution but can reduce growth when timed after the bolting stage and before seed production.
- Dicamba and 2,4-D are most commonly used to control Yellow Starthistle.
- Picloram has also been deemed effective but is not suitable for wet, coastal soils.
- For maximum efficacy, apply from the seedling to bolt stages.
- We recommend that any herbicide application is carried out by a person holding a valid BC Pesticide Applicator Certificate. Before selecting and applying herbicides, you must review and follow herbicide labels and application rates; municipal, regional, provincial and federal laws and regulations; species-specific treatment recommendations, and site-specific goals and objectives.
- There are no current biological controls for this plant in BC. However, numerous agents exist in the U.S, such as Bud Weevil, Hairy Weevil, Gallfly, and Flower Weevil.
- Canadian Food Inspection Agency. Yellow Starthistle – Centaurea solstitialis. https://inspection.canada.ca/plant-health/plant-pests-invasive-species/invasive-plants/fact-sheets/yellow-starthistle/eng/1331825936442/1331826040057
- Coastal Invasive Species Committee. Yellow Starthistle. https://www.coastalisc.com/yellow-starthistle/
- Government of BC, A Guide to Weeds in British Columbia, “Yellow Starthistle” https://www2.gov.bc.ca/assets/gov/environment/plants-animals-and-ecosystems/invasive-species/alerts/yellow_starthistle.pdf
- Plumas-Sierra Noxious Weeds Management Group. Yellow Starthistle. https://www.plumascounty.us/DocumentCenter/View/1587/starthistle?bidId=
- United State Department of Agriculture. Field Guide for Managing Yellow Starthistle in the Southwest. https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5410133.pdf
- Washington State Noxious Weed Control Board. Yellow Starthistle. https://www.nwcb.wa.gov/weeds/yellow-starthistle