Yellow star thistle, geeldissel, golden star thistle, St. Barnaby's thistle, yellow centaury, yellow cockspur
Yellow Starthistle was recently found in Beaverhead County and has been reported in other counties in recent years, but has been eradicated. Yellow starthistle is a relative of knapweed and its yellow flowers resemble the pink knapweed flower. This plant is an annual that can grow up to three to five feet in height. Leaves and stems are a grayish-green color and leaves are covered with a cottony wool. Lower leaves are up to 3 inches long and deeply lobed, while upper leaves are short and narrow with fewer lobes and give the stems a “winged” appearance. Flowers are a bright yellow and sharp spines up to ¾ inches in length surround the base of the flower. Starthistle primarily spreads by seed, and each plant can produce up to 150,000 seeds.
The bright yellow, knapweed-looking flower, and the sharp spines that have been known to puncture tires.
Plants typically thrive in full sunlight with deep, well-drained soils. It is often found in disturbed areas, roadsides, rangelands , waste areas, overgrazed lands, pastures, hay fields, along waterways, roadsides, forests and other non-crop areas.
Currently found in the following counties:
Yellow starthistle is poisonous to horses. When ingested, the plant causes a neurological disorder called equine nigropallidal encephalomalacia or chewing disorder. If horses continue to feed on yellow starthistle, brain lesions and mycosal ulcers in the mouth may form which eventually leads to death. Yellow starthistle Was found in two counties in Montana in 2010.
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Photo Credits: Chris Bersbach; Charles Turner, USDA Agricultural Research Service, Bugwood.org; C. Azuma, ASLA, www.flickr.com/photos/azumac/; University of Idaho Archive, University of Idaho, Bugwood.org