ReproductionA single yellow starthistle plant is capable of producing over 150,000 seeds per season. These seeds can spread to new locations: by wind, as a contaminant in domestic seed, by construction, farm and other vehicles and equipment, by people and animals or merely drop to the ground to re-infest the surrounding area. Seeds may lay dormant in the soil for long periods, resulting in a large seed bank. HabitatAlthough yellow starthistle will survive and form healthy infestations in most locations including coarse, shallow soils with as little as 25 cm annual precipitation, it prefers low elevations, level areas or south facing slopes with deep, well drained, deep silty loam soils receiving 40 - 80 cm annual precipitation. Over-utilized grasslands are particularly susceptible to yellow starthistle invasion. ConcernPrimarily a rangeland weed, yellow starthistle is very competitive and forms dense infestations when left uncontrolled. This severely reduces the diversity of native plant communities and reduces production of forage for livestock and wildlife. It is also known to infest perimeters of cropland where it reduces crop yield, quality and may hinder harvesting. Yellow starthistle causes a neurological disorder in horses known a 'chewing disease'. After ingesting yellow starthistle a toxin is produced which affects the horses nerve system disrupting eating and drinking functions. Death is often the result and there is no known cure.
Photos courtesy Dr. Ben Roche, Washington State University, Pullman, Washington
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