| Centaurea solstitialis Yellow star-thistle |
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|---|---|
| Yellow Star-thistle flower | |
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| (unranked): | Asterids |
| Order: | Asterales |
| Family: | Asteraceae |
| Tribe: | Cynareae |
| Genus: | Centaurea |
| Species: | C. solstitialis |
| Binomial name | |
| Centaurea solstitialis L. |
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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) [1] The plant is a thorny winter annual species in the knapweed genus.
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Centaurea solstitialis is a grayish-green plant with multiple rigid stems that extend in all directions from the base, forming a bushy-looking cluster that can reach 2 metres (6.6 ft) in height and more than that in diameter. It produces bright yellow flowers ringed with long, sharp spines. The plant grows quickly and is very competitive. It bears a taproot that can reach 1 metre (3.3 ft) deep into the soil, allowing it to thrive during dry, hot summers. It is versatile in its growth patterns, and can adapt to drought or low soil moisture content by producing smaller plants with fewer seeds during dry years.
Yellow star-thistle is a plant toxic to horses, causing chewing disease (Nigropallidal encephalomalacia).[2]
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.[3]
The introduction of Centaurea solstitialis, Yellow Star-thistle, 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).[4]
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.
After the turn of the 20th century, Spain, France, Italy, and perhaps Turkestan were also likely sources of the invasion's seed.[4] Since its introduction to California in the mid-nineteenth century,[4] 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. [5][6]
By 1970,[6] yellow star-thistle had reached 23 U.S. states.[4] 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). [7] The plant is considered an invasive species in six of the 41 states: California, Oregon, Washington, Idaho, Utah, and New Jersey.
Most herbicides used for controlling Yellow Star-thistle are registered for rangelands, 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 (ie: 'Round-Up') 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.[8]
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.[9] Resistance was discovered to be conveyed by a single nuclear recessive gene.[10]
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. [11][12]
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.[22] The rust causes widespread pathology in the leaves of the plant and slow its dispersal.
Grazing by goats, cattle, or sheep can be effective in controlling Yellow star-thistle.[23] Goats will eat star-thistle even in its spiny stage.[24]
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.[25] 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).[26]
Species similar to Centaurea solstitialis are Red Star thistle—Centaurea calcitrapa, and Rough Star-thistle—Centaurea aspera.[27]
