Family: Asteraceae (Aster Family)
Duration and Habit: Annual, Biennial Herb
DiTomaso (2001) states that C. melitensis is an erect winter annual with a spiny, yellow-flowered head that typically reaches 1 m tall. The stems are stiff and openly branched from near or above the base or sometimes not branched in very small plants. Stem leaves are alternate, and mostly linear or narrowly oblong to oblanceolate. Margins are smooth, toothed, or wavy, and leaf bases extend down the stems (decurrent) and give stems a winged appearance. Rosette leaves typically are withered by flowering time.
Ecological Threat: When star thistle infestations are high, native species can experience drought conditions even in years with normal rainfall (Gerlach et al., 1998, in DiTomaso, 2001).
Biology & Spread: DiTomaso (2001) reports that C. melitensis is insect-pollinated and reproduces by seed. Seed production is highly variable. Plants can produce 1-60 or more seeds per head and 1-100 heads or more per plant.
U.S. Habitat: Occurs in open, disturbed sites such as grasslands, rangeland, open woodlands, fields, pastures, roadsides, waste places and fields.
U.S. Nativity: Introduced to U.S.
Native Origin: Europe and North Africa
U.S. Present: AL, AZ, CA, GA, HI, IN, MA, MO, NJ, NM, NV, OR, PA, SC, TX, UT, WA, WI
Distribution: It is found to be invasive along the western coast and elsewhere in the United States (USDA-NRCS 2003).
List All Observations of Centaurea melitensis reported by Citizen Scientists
Resembles: Centaurea solstitialis
Methods used to control yellow star thistle (Centaurea solstitialis) can be applied. A variety of methods are available for managing yellow starthistle, ranging from biological, chemical, and mechanical. For this reason, an integrated weed management plan, including tactics to prevent the spread of yellow starthistle outside of infested areas, is recommended. For example, when driving, walking, or moving livestock through infested areas, clothing, vehicles, and animals should be inspected and cleaned to remove any seeds before continuing on into uninfested areas.
Biological Control: Six biological control insects have been released in the United States for yellow starthistle control: Bangasternus orientalis, Eustenopus villosus, Urophora jaculata, Urophora sirunaseva, Larinus curtus, and Chaetorellia australis. Of these, five became established and three (B. orientalis, U. sirunaseva and E. villosus) are widespread. Also, the accidentally introduced fly, Chaetorellia succinea has a strong affinity to yellow starthistle and is found almost everywhere yellow starthistle occurs. All of these insects attack the seedhead of yellow starthistle, effectively limiting the number of seeds the plants are able to produce. Current research indicates that the insects have reduced seed yield by at least 50%. The rust fungus, Puccinia juncea var. solstitialis was released in California in 2003. It is too early to know if this rust will establish and eventually cause high mortality of yellow starthistle in the wild. Several more fungi and insects are currently being tested for introduction into the United States.
Chemical Control: Application of the systemic herbicides clopyralid or picloram between December and April seems to be the most effective. Application during the winter encourages the growth of other, more desirable, plants.
Mechanical Control: Mowing is effective during the early flowering stage or when most buds have produced spines. However, it is only successful when no leaves are present below the level of the cut.
Grazing: Sheep, goats, and cattle can graze on yellow starthistle in early spring, before the flower?s spines develop. Goats will also graze plants in the spiny or flowering stages. Grazing reduces biomass and seed production.
For more information on the management of yellow starthistle, please contact:
Joe DiTomaso, University of California-Davis, firstname.lastname@example.org Weed Records and Information Center (WeedRIC) - Yellow Starthistle http://wric.ucdavis.edu/yst
The University of California Pest Management Guides - Yellow Star-thistle http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7402.html
Encycloweedia - http://pi.cdfa.ca.gov/weedinfo/centaurea2.htm
Yellow Starthistle Information (DiTomaso, 2001), Global Invasive Species Database (http://www.issg.org/database)
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