*Centaurea solstitialis* L. (Yellow star-thistle )
Steve Dewey, Utah State University, Bugwood.org		Family: Asteraceae (Aster Family) Synonym(s): Leucantha solstitialis Duration: Annual Habit: Herb Listed by: Invasive Plant Atlas of the US: 1 Federal Noxious Weed: 0 TDA Noxious Weed: 0 TPWD Prohibited Exotic Species: 0
Description: Yellow starthistle is an annual herbaceous plant. Plants are gray-green to blue-green, grow from 6 in. to 5 ft. (15 cm to 15 dm) in height, and have deep taproots. Flowers are bright yellow with sharp spines surrounding the base, giving the plant a particularly menacing appearance and a painful response if touched. Stems and leaves are covered with cottony wool. Basal leaves are 2 to 3 in. (6 ? 7 cm.) long and deeply lobed . Upper leaves are short (0.5 to 1.0 in.; 1 to 2.5 cm) and narrow, with few lobes. History: Yellow starthistle was probably introduced into the United States through contaminated alfalfa in the mid-1800?s. Biology & Spread: Spread of yellow starthistle is by seed and each seedhead can produce from 35 to approximately 80 seeds. However, the seeds have no wind-dispersal mechanisms so few seeds move more than two feet from the parent plant without assistance. Therefore, animals and human influences, such as vehicles, contaminated crop seed, hay or soil, and road maintenance, contribute greatly to the plant?s rapid and long-distance spread. Ecological Threat: Yellow starthistle is a strong invader that has been found in nearly every county in California and appears to be moving north and eastward. Some specialists liken its invasion to that of leafy spurge in North Dakota and Montana. As the plant infests an area, it chokes out the native plants, reducing biodiversity and wildlife habitat and forage. Another concern associated with the plant is ?chewing disease? that develops in horses that have eaten yellow starthistle. This disease affects horses? nervous system and is usually fatal. Yellow starthistle does best in areas with a summer drought. It has been present in the Mid-West and eastern US for decades but has not built up high densities and is not considered a threat to areas with summer rainfall which includes most of the area east of the Rocky Mountains. US Habitat: Yellow starthistle is found typically in full sunlight and deep, well-drained soils, where annual rainfall is between 10-60 inches, and is especially common in disturbed areas such as roadsides. Distribution US Nativity: Introduced to U.S. Native Origin: Africa, temperate Asia, Europe US States: AZ, CA, CO, CT, DE, FL, IA, ID, IL, IN, KS, KY, MA, MD, MI, MN, MO, MT, NC, ND, NE, NH, NJ, NM, NV, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VA, WA, WI, WV, WY Resembles/Alternatives: Management: 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, ditomaso@vegmail.ucdavis.edu USE PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY, FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS OR RECOMMENDATIONS. MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL. Listing Source Texas Department ofAgriculture Noxious Plant List Texas Parks and Wildlife Department Prohibited Exotic Species Invaders Program Federal Noxious Weed Union of Concerned Scientists United States Forest Service Southern Research Station Text References Bossard, Carla C., John Randall, and Marc C. Hashovsky. Invasive Plants of California Data Source APWG WeedUS Database https://www.cabidigitallibrary.org/doi/10.1079/cabicompendium.12043 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 Last Updated: 2024-02-05 by Ashley Morgan-Olvera, TISI