Yellow Starthistle Centaurea solstitialis L. Common Names: Golden star thistle, St. Barnaby’s thistle, yellow centaury, yellow cockspur and geeldissel

What is Yellow Star Thistle? Yellow star thistle is an annual dicot with several erect branches that each contain a flowering head covered in thorny bracts.

What is Yellow Star Thistle? Classification: Kingdom Plantae – Plants Subkingdom Tracheobionta – Vascular plants Superdivision Spermatophyta – Seed plants Division Magnoliophyta – Flowering plants Class Magnoliopsida – Dicotyledons Subclass Asteridae Order Asterales Family Asteraceae – Aster (Sunflower) family Genus Centaurea L. – knapweed Species Centaurea solstitialis L. – yellow star-thistle

Why is it Bad? The thorns on the head of the star thistle interfere with livestock grazing, recreation and wildlife management Yellow Star Thistle is also toxic to horses and can cause a potentially fatal disorder called “chewing disease.” Reduction of biodiversity due to displacement of native vegetation. Linda M. Wilson, Cynthia Jette, John Connett, Joseph P. McCaffrey Biology and Biological Control of Yellow Starthistle. USDA Forest Service FHTET nd Ed.

Why is it Bad?

Life History- Yellow Star Thistle Seed germination in the fall and development into overwintering rosettes. Rapid growth in late spring with stalk growth each with a flower bud. Yellow flowers bloom in early summer. By late summer the plant begins to dry.

Life History- Yellow Star Thistle Seeds dipersed by wind, water or by clinging to fur or clothing during the late summer and early fall. Yellow star thistle continues to dry over winter and eventually loses its thorny bracts and dies.

Native Land & U.S. Introduction Yellow star thistle is native to Eurasia. Introduced to the U.S. in the 1800s through accidentally contaminated seeds.

U.S. Distribution

States where C. solstitialis is Listed as Invasive California, Idaho, Oregon, Utah, Washington, Arizona, Colorado, Montana, New Mexico, Nevada, North Dakota and South Dakota.

Control Grazing Cattle, sheep and goats will graze on yellow star thistle until it develops thorns. Toxic to horses. Low nutritional value Cattle with high yellow star thistle diet lose weight. (Callihan and others 1982)

Control Mechanical Manual removal- Effective on small patches before seed production. Tillage- Can quickly reduce yellow star thistle seed bank, but can do the same to desirable species. Mowing- Too early or too late can increase the yellow star thistle infestation. Too early- Mowing can remove early competition by natives. Too late- Mowing can scatter yellow star thistle seeds.

Control Fire Control Prescribed burns are not effective. Fire will kill the plant but not the seeds and may stimulate seed growth Yellow star thistle thrives in areas with increased sunlight, soil surface, bare soil and decreased competition.

Control Chemical Picloram is the most widely used in the western states. Not registered for use in California. Clopyralid is effective for control and least damaging to grasses.

Control Chemical cont. Picloram resistance observed in yellow star thistle in frequently treated areas. Most effective when used on early growth. It is important to incorporate other modes of control.

Biological Control- Weevils Bangasternus orientalis (seedhead weevil)- attacks the early bud stages Eustenopus villosus (hairy weevil)- Feeds on mid- stage buds and lays eggs in late-stage buds Larinus curtus (flower weevil)- Lays eggs in open flowers

Case Study

Biological Control- Flies Chaetorellia australis (peacock fly)and C. succinea (false peacock fly)- feeds on seedheads Urophora siruneseva(seadhead fly)- Forms galls in seedheads C. Succinea- accidentally released and not approved due to damage to safflower.

Costs Ecological Dense populations of yellow star thistle use deep soil water earlier than natives. Natives can experience drought conditions in years with normal rainfall. (Benefield et. al., 2001) and (Gerlach et. al., 1998.)

Costs Economic Interference with: Livestock grazing Forage harvesting procedures Lower yield and forage quality

Is it Good? Honey An important honey source in California and other western states Medicine Used in Turkish folk medicine for ulcer treatment. Lab tests of flower extract show significant antiulcerogenic activity in rats.

Questions ?

References Benefield, Carri B.; DiTomaso, Joseph M.; Kyser, Guy B Impacts of yellow starthistle density on the soil moisture profile and rangeland management. Proceedings, Western Society of Weed Science. 51: 66. [40408] Bussan, Alvin J.; Dyer, William E Herbicides and rangeland. In: Sheley, Roger L.; Petroff, Janet K., eds. Biology and management of noxious rangeland weeds. Corvallis, OR: Oregon State University Press: [35716] Carlson, John E.; Willis, David B.; Michalson, Edgar L.; Callihan, Robert H Yellow starthistle in north-central Idaho: a survey of farmers' and ranchers' behavior and attitudes. Bulletin No Moscow, ID: University of Idaho, College of Agriculture, Agricultural Experiment Station. 11 p. [40405] DiTomaso, Joe Element stewardship abstract: Centaurea solstitialis L. In: Weeds on the web: The Nature Conservancy wildland invasive species program, [Online]. Available: [2001, December 19]. [40416] Gerlach, John; Dyer, Andrew; Rice, Kevin Grassland and foothill woodland ecosystems of the Central Valley. Fremontia. 26(4): [40400]

References Hastings, Marla S.; DiTomaso, Joseph M Fire controls yellow starthistle in California grasslands. Restoration and Management Notes. 14(2): [40398] Linda M. Wilson, Cynthia Jette, John Connett, Joseph P. McCaffrey Biology and Biological Control of Yellow Starthistle. USDA Forest Service FHTET nd Ed. Maddox, Donald M.; Mayfield, Aubrey; Poritz, Noah H Distribution of yellow starthistle (Centaurea solstitialis) and Russian knapweed (Centaurea repens). Weed Science. 33: [23467] Yesilada, Erdem; Sezik, Ekrem; Fujita, Tetsuro; [and others] Screening of some Turkish medicinal plants for their antiulcerogenic activities. Phytotherapy Research. 7(3): [28718] Zouhar, Kris Centaurea solstitialis. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: [ 2008, December 8].