Yellow Starthistle WEED ALERT

Yellow Starthistle (Centaurea solstitialis)
WEED ALERT

Yellow starthistle is a continuing threat to British Columbia from adjacent infestations in Washington and Idaho states where it infests over 1.25 million acres. In California it infests over 800 million acres. To date, only one isolated plant has been found in BC (Kamloops). It will invade areas ranging from roadsides and disturbed areas to undisturbed, healthy grasslands. It prefers disturbed sites like roadsides, unused areas and over-utilized pastures and rangeland. Be on the look out for this invasive weed, particularly along southern borders.

Biology

Normally a winter annual, yellow starthistle begins growth as a small seedling in the fall, is dormant during winter and begins re-growing the next spring. It will increase in size as a low growing rosette and from May to June begin growing from 0.6 to 1 metre in height. Stems are winged and covered in fine hair. Single buds develop at the end of each branch stalk in June and July. From mid July to August flowers armed with sharp thorns appear with seeds maturing in late summer. Two seed types, plumed and plumeless, are produced. Seeds with a white, parachute type of plume spread to new locations on the wind while plumeless seeds drop near the plant to re-infest the site.

Sharp spines on flowerhead bracts

Reproduction

A 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.

Habitat

Although 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.

Concern

Primarily 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.

Devastation on grassland

Photos courtesy Dr. Ben Roche, Washington State University, Pullman, Washington

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Yellow Starthistle (Centaurea solstitialis) WEED ALERT

Biology

Reproduction

Habitat

Concern

Yellow Starthistle (Centaurea solstitialis)
WEED ALERT