Yellow Starthistle

Yellow Starthistle (Centaurea solstitialis L.)

Report

Photo Credit: S. Dewey, Utah State University, Bugwood.org

Management Category

Synonyms

St. Barnaby’s thistle
Geeldissel
Golden star thistle
Yellow centaury
Yellow cockspur
Maltese star thistle

ID Characteristics

General: Yellow starthistle is a winter annual and occasional biennial in the Asteraceae (sunflower/daisy) family.

Flowers: Are yellow and thistle-like, growing alone 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. The stems are dull green, rigid, branching, winged and covered in woolly hair.

Leaves: Basal (rosette) leaves are alternate and lobed with smooth margins; they resemble dandelion leaves. Stem leaves are entire and sharply pointed with wavy margins.

Fruits: Starthistle produces two types of 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.

Similar Species

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. It was introduced to North America through contaminated seed in the 1800’s.

Yellow starthistle 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. It is commonly found in rocky, shallow soils.

How it Spreads

Yellow starthistle reproduces exclusively by seed. The plant typically produces 700 – 1000 seeds, which may lay dormant in the soil for up to 10 years. However, vigorous plants are capable of producing up to 170,000 seeds.

The 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.

Impacts

Ecological:

Possesses pioneering capabilities.
Deters the growth of other plants around it (allopathic effect).
Displaces native vegetation, thus reducing biodiversity.

Economic:

Poisonous to horses and harmful to grazing cattle.
Dense infestations reduce forage availability and quality.
Dense stands impede recreational access.

Prevent the Spread

Yellow starthistle is not yet found in the Sea to Sky region, but is found in neighbouring areas and may arrive here soon. The goal is to prevent Yellow starthistle’s introduction by focusing on education and awareness. If prevention fails, the goal will become immediate eradication following the proposed SSISC EDRR protocol.

Learn to identify yellow starthistle: use the images presented on this page to learn how to identify yellow starthistle.

What to do if you spot it: You can report any yellow starthistle sighting by visiting our reporting page.

DO:

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.

DO NOT:

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.

Control

Mechanical

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, though it can reduce growth if it is done after the bolting stage and before seed production.

Chemical

Aminopyralid, clopyralid, glyphosate, 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.

Biological