|Yellow Star-thistle flower|
Centaurea solstitialis, yellow star-thistle, is a member of the Asteraceae family, native to the Mediterranean Basin region. The plant is also known as golden starthistle, yellow cockspur and St. Barnaby's thistle (or Barnaby thistle) The plant is a thorny winter annual species in the knapweed genus.
|This section requires expansion. (May 2013)|
Invasive species 
Centaurea solstitialis grows as a balanced part of the ecology in Eurasia, where it is kept in check by an assortment of natural herbivore enemies and other plants that have co-evolved with it in its native habitat. In regions of North America, without these natural biological controls, it has become an invasive species and noxious weed.
The Yellow star-thistle plant has the ability to create monotypic stands and habitats in the cultivated soil of fields, graded dirt sites, and disturbed natural ecosystem lands. Its colonization eliminates and prevents other plant species from growing terminating the habitat's biodiversity. Extensive spreading monotypic fields of yellow starthistle are not uncommon. Its growth plasticity, competitiveness, preference for the Mediterranean climate, and a lack of natural herbivore enemies and co-evolved species, make it a very successful invader. The plant is an invasive pest in field crops, degrades native plant habitats and natural ecosystems, prevents the grazing of domestic animals in rangelands, and is a physical barrier to indigenous animal movement in wildlands.
Species introduction 
The introduction of Centaurea solstitialis in North America probably occurred in California sometime after the start of the California Gold Rush, as a fodder seed contaminant in imported Chilean-harvested alfalfa seed, also known as Chilean clover (Trifolium macraei).
Yellow star-thistle was dispersed into agricultural fields in California, and immediately took hold in the state's Mediterranean-type climate areas. Human factors, such as mowing, land grading for development and roads, domestic animal grazing, and disturbance of the soil surface for agricultural tillage and wildland firebreaks have and continue to contribute to the successful thriving and spread of this plant. Yellow starthistle is now a very common sight in vacant lots and fields, along roadsides and trails,in pastures and ranch lands, and in parks, open-space preserves and natural areas.
Range increase 
After the turn of the 20th century, Spain, France, Italy, and perhaps Turkestan were also likely sources of the invasion's seed. Since its introduction to California in the mid-nineteenth century, it has become a large-scale invasive species (noxious weed or invasive exotic) throughout twenty-three states. It currently dominates over 15,000,000 acres (61,000 km2) in California alone.
By 1970, yellow star-thistle had reached 23 U.S. states. According to the USDA Forest Service, as of 2006 the plant has been reported present in 41 of the 48 contiguous U.S. states, with the only exceptions being Maine, Vermont, and five of the Deep South states (Arkansas, Louisiana, Mississippi, Alabama, and Georgia). The plant is considered an invasive species in six of the 41 states: California, Oregon, Washington, Idaho, Utah, and New Jersey.
Chemical control 
Most herbicides used for controlling Yellow Star-thistle are registered for range lands, right-of-way, and other non-crop areas. Many auxin-like or growth-regulator herbicides are used for post-emergence control, including 2,4-D, aminopyralid, clopyralid, dicamba, picloram and triclopyr. Alternatively, glyphosate (e.g., Monsanto "Roundup") may be used. Pre-emergence herbicides used for yellow star-thistle control include chlorsulfuron and sulfometuron. Pre-emergence and post-emergence herbicides may be used effectively together to kill growing plants as well as any new seedlings that may emerge from the copious soil seed bank often produced by yellow starthistle. Controlled burning may also be used in conjunction with clopyralid application as an effective integrated approach to yellow star-thistle management.
A yellow star-thistle biotype resistant to picloram was discovered in a pasture near Dayton, Ohio in 1988. This biotype was determined to have cross resistance to other auxin-like herbicides, especially clopyralid. Resistance was discovered to be conveyed by a single nuclear recessive gene.
Biological control 
Yellow star-thistle is sometimes resistant to removal methods such as mowing and burning, because of its long root system and the seeds' ability to withstand fire. The plant has been the target of biological pest control programs with positive results. Seven types of seed-feeding insects have been released (one accidentally) to control the plant.
- Three species of weevil in the beetle subfamily Cleoninae effectively reduce seed production in the yellow star-thistle.
- Yellow star-thistle bud weevil (Bangasternus orientalis) is a fuzzy brown weevil that lays its eggs in the flowers, and when its larvae hatch, they feed on the developing seed.
- Yellow starthistle hairy weevil (Eustenopus villosus) is a long-snouted, hairy-looking weevil that lays a single egg inside each flower bud. The larva then consumes the seeds within.
- Yellow star-thistle flower weevil (Larinus curtus) is a brownish weevil that lays eggs in the flowers as it feeds on the pollen. The larvae then eat the seeds when they hatch. This insect has failed to established dense populations in the United States.
- Four species of tephritid fruit fly also attack the seedheads of yellow star-thistle.
- Yellow star-thistle peacock fly and false peacock fly (Chaetorellia australis and Chaetorellia succinea, respectively, the latter released unintentionally) are small nectar-feeding flies that deposit eggs into the seedheads, where their larvae consume the seeds and flower ovaries.
- Banded yellow star-thistle gall fly (Urophora sirunaseva) produces larvae that pupate within a woody gall within the flower and disrupt seed production.
- Another gall fly Urophora jaculata was released in 1969 but never established.
- Rust fungus
Additionally, a variety of the rust fungus Puccinia jaceae var. solstitialis, first released in July 2003 on a ranch in the Napa Valley, has shown promise as an agent against yellow star-thistle. The rust causes widespread pathology in the leaves of the plant and slow its dispersal.
Although these biocontrol agents have proven somewhat effective at controlling Centaurea solstitialis, there is interest in finding additional agents to further control the species. Two weevils, including Larinus filiformis, a flowerhead feeding weevil, and Ceratapion basicorne (Illiger) (Coleoptera: Apionidae), which develops in the root crown of rosettes have been evaluated and proposed for introduction. Also under evaluation are a stem-feeding flea beetle Psylliodes chalcomera (Illiger) (Coleoptera: Chrysomelidae) (Cristofaro et al. 2004a), a lacebug Tingis grisea Germar (Heteroptera: Tingidae), and a mite Aceria solstitialis de Lillo (Acari: Eriophyidae). (de Lillo et al. 2003).
Similar species 
See also 
- DiTomaso, J (2001). "Element Stewarship Asbtract for Centaurea solstitialis". The Nature Conservancy. Archived from the original on 2007-02-21. Retrieved 2007-06-01.
- Yellow Starthistle species profile from the U.S. Department of Agriculture National Invasive Species Information Center
- Yellow Starthistle Information from a University of California, Davis (UCD) website
- PDF (286 KiB), Mount Diablo Interpretive Association. Retrieved on 2008-10-15.
- 1970 UCD Yellow Starthistle Information website - Map of Distribution of yellow star-thistle in the U.S.[dead link]
- PDF (179 KiB), USDA Forest Service. Retrieved on 2008-10-15.
- "UC IPM Online". Ipm.ucdavis.edu. 2005-05-20. Retrieved 2012-04-28.
- Fuerst E.P., Sterling T.M., Norman M.A., Prather T.S., Irzyk G.P., Wu Y., Lownds N.K., and Callihan R.H., 1996. Physiological characterization of picloram resistance in yellow star-thistle. Pest Biochem Physiol 56:149–161.
- Sabba R.P., Ray I.M., Lownds N. and Sterling T.N., 2003. Inheritance of resistance to clopyralid and picloram in yellow star-thistle (Centaurea solstitialis L.) is controlled by a single nuclear recessive gene. J. Heredity 94(6): 523-527.
- "Biology and Biological Control of Yellow Starthistle" (PDF). Retrieved 2012-04-28.
- Pitcairn, M. J., B.Villegas, D. M. Woods, R. Yacoub, and D. B. Joley. 2008. Evaluating implementation success for seven seed head insects on Centaurea solstitialis in California, USA, pp. 610-616. In M. H. Julien, R. Sforza, M. C. Bon, H. C. Evans, P. E. Hatcher, H. L. Hinz, and B. G. Rector (eds.), Proceedings of the XII International Symposium on Biological Control of Weeds. La Grande Motte, Montpellier, France (in press).
- Campobasso, G.; Sobhian, R.; Knutson, L.; Terragitti, G. 1998. Host specificity of Bangasternus orientalis Capiomont (Coleoptera: Curculionidae) introduced into the United States for biological control of yellow starthistle (Centaurea solstitialis L., Asteraceae: Carduae). Environmental entomology,. v. 27 (6), p. 1525-1530.
- Fornasari, L., and R. Sobhain. 1993. Life history of Eustenopus villosus (Coleoptera’ Curculionidae), a promising biological control agent for yellow starthistle. Environ. Entomol. 22: 684-692.
- Connett, J.F.; Wilson, L.M.; McCaffrey, J.P.; Harmon, B.L. 2001. Phenological synchrony of Eustenopus villosus (Coleoptera: Curculionidae) with Centaurea solstitialis in Idaho. Environmental entomology, v. 30 (2), p. 439-442.
- Fornasari, L. and C.E. Turner. 1992. Host specificity of the Paleartic weevil Larinus curtus Hochut (Coleoptera: Curculionidae), a natural enemy of Centaurea solstitialis L. (Asteraceae: Cardueae). In: Proceedings of the Eighth International Symposium on Biological Control of Weeds. 2–7 February 1992. Lincoln University, Canter- 1bury, New Zealand, 385-391
- Pitcairn, M. J., G. L. Piper, and E. M. Coombs. 2004. Yellow starthistle, pp. 421-435. In E. M. Coombs, J. K. Clark, G. L. Piper, and A. F. Cofrancesco, Jr. (eds.), Biological control of invasive plants in the United States. Oregon State University Press, Corvallis, OR
- Pitcairn, M. J., D. M. Woods, and V. Popescu. 2005. Update on the long-term monitoring of the combined impact of biological control insects on yellow starthistle, pp. 27-30. In D. M. Woods (ed.), Biological control program annual summary, 2004. California Department of Food and Agriculture, Plant Health and Pest Prevention Services, Sacramento, CA
- Turner, C.E., G.L. Piper and E.M. Coombs. 1996. Chaetorellia australis (Diptera: Tephritidae) for biological control of yellow starthistle, Centaurea solstitialis (Compositae), in the western USA: establishment and seed destruction. Bull. Entomol. Res. 86: 1 77-182.
- Sobhian, R. 1993. Life history and host specificity of Urophora sirunaseva (Herng)(Dipt., Tephritidae), an agent for biological control of yellow starthistle, with remarks on the host plant. J. Appl. Entomol. 116: 381-390.
- Turner, C.E., Johnson, J.B., McCaffrey, J.P., 1994. Yellow starthistle, Centaurea solstitialis L. (Asteraceae). In: Nechols, J.R. (Ed.), Biological Control in the U.S. Western Region: Accomplishments and Benefits of Regional Research Project W-84 (1964-1989). Division of Agriculture and Natural Research, University of California, Berkeley, pp. 274–279
- Fungus Unleashed To Combat Yellow Star-thistle from the U.S. Department of Agriculture website
- [dead link]
- "Yellow Starthistle Management Guidelines-UC IPM". Ipm.ucdavis.edu. 2005-05-20. Retrieved 2012-04-28.
- Smith, L. 2007. Physiological host range of Ceratapion basicorne, a prospective biological control agent of Centaurea solstitialis (Asteraceae). Biol. Control 41: 120-133.
- Smith, L. 2004. Prospective new agents for biological control of yellow starthistle, pp. 136-138. Proceedings 56th Annual California Weed Science Society, 12–14 January 2004, Sacramento, CA
- Rose, Francis (1981). The Wild Flower Key. Frederick Warne & Co. pp. 386–387. ISBN 0-7232-2419-6.
- USDA - " Larinus filiformis as a Biological control agent for Centaurea solstitialis (flowerhead feeding weevil)
- Balciunas, J. K., and B. Villegas; "Unintentionally released Chaetorellia succinea (Diptera: Tephritidae): Is this natural enemy of yellow starthistle a threat to safflower growers?"; Environ. Entomol 30: 953-963; pub. 2001.
|Wikimedia Commons has media related to: Centaurea solstitialis|
- Species Profile--Yellow Star Thistle (Centaurea solstitialis), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Yellow Star Thistle.
- USDA Profile - Centaurea solstitialis (yellow star-thistle)
- U.C. Jepson Manual treatment - Centaurea solstitialis
- California Integrated Pest Control - Biocontrol of Centaurea solstitialis -Yellow star-thistle
- Centaurea solstitialis - U.C. CalPhoto gallery
- Texas AgriLife Extension - Toxic Plants of Texas - Starthistles - Yellow Starthistle is toxic to horses