Other Common Names: St. Barnaby’s thistle, yellow cockspur. ... For more details check out the Invasive Species Compendium datasheet on Centaurea solstitialis (yellow starthistle). Impacts:Agricultural: Infestations can reduce forage quality and forage availability in pastures and in hay. Yellow starthistle is an invasive herbaceous annual or biennial of the Asteraceae family that spreads by seeds, forming dense stands in open, sunny areas (Maddox, 1981). Bangasternus orientalis, or the yellow starthistle bud weevil, reduces seed production of yellow starthistle plants by 50 to 60%. Invasive plants should never be considered as forage. yellow star-thistle in the bolting stage but, before the flower’s spines develop. Perennial grasses can compete against yellow starthistle invasions, particularly species that can initiate growth in the fall. Yellow starthistle is in the Asteraceae family and is a long-lived winter annual; Stems are erect, rough, branching and can grow up to 1 m in height. Invasive Plant Species of West Virginia Jil M. Swearingen, Survey of invasive plants occurring on National Park Service lands, 2000-2007 John Randall, The Nature Conservancy, Survey of TNC Preserves, 1995. Sometimes it can grow in clusters that appear shrubby. Consult the PLANTS Web site and your State Department of Natural Resources for this plant’s current status (e.g., threatened or endangered species, state noxious status, and wetland indicator values). Yellow starthistle, Centaurea solstitialis, is a particularly nasty type of invasive knapweed in the Aster family. It has taken over vast areas of land in the western United States with estimates of over 15 million acres in California, 280,000 acres in Idaho, and 135,000 acres in Oregon. Adults overwinter outside the host plant, leaving their … Growth Form/Reproduction: Winter annual. It is poisonous to horses. Yellow star-thistle is a listed noxious weed and is invasive in many western states. Seed. It is easily recognizable from its brilliant yellow flowers, and cactus like spines. Spotted knapweed, Centaurea stoebe spp. Dense populations of this plant result in lowered yield and quality of forages and occasionally crops. Weed Seed - Yellow Starthistle (Centaurea solstitialis) Plant pest card - Yellow starthistle. Origin: Europe. In deep-soiled rangelands Yellow Starthistle roots grow fast and deep (Sheley and Petroff 1999). Centaurea solstitialis Photo courtesy Bob Case. However, Yellow Starthistle growth rates can decline as its density increases. Overgrazing will reduce the ability of other vegetation to recover and shade out the starthistle. Yellow Starthistle Centaurea solstitialis L. Sunflower family (Asteraceae) NATIVE RANGE Africa, temperate Asia and Eurasia (Balkan-Asia Minor, the Middle East and south-central Europe) Mediterranean region of southern Europe and northern Africa, especially Turkey DESCRIPTION Yellow starthistle is an annual herbaceous plant. Yellow starthistle is an invasive plant found in pastures and rangelands. Grazing reduces biomass and seed produc-tion. Genetics Yellow starthistle is diploid (2n=16), with a large amount of genetic variation (Sun, 1997; Sun and Ritland, 1998). Adults cause minor defoliation, with the majority of the damage caused by larval feeding. Yellow starthistle inhabits open hills, grasslands, open woodlands, fields, roadsides, and rangelands, and it is considered one of the most serious rangeland weeds in the state. Common names: yellow starthistle Centaurea solstitialis (yellow starthistle) is a bushy winter annual (family Asteraceae) that invades 12 million acres in California. 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