IDENTIFICATION
Provincial Noxious. Winter annual.
Yellow starthistle has winged, heavily branched, rigid stems covered
in cottony hairs. The blossoms are bright yellow, single flowerheads with
long, sharp, straw-coloured thorns and the upper leaves are small and
sharply pointed. Mature plants are 0.6 - 0.9 m tall.
DAMAGE
In horses, yellow starthistle causes a neurological disorder called
"chewing disease." It establishes easily on disturbed land and
forms dense infestations that reduce the available forage for livestock
and wildlife. It may have allelopathic effects on some associated native
species.
HABITAT
Yellow starthistle can invade rangelands, pastures, roadsides,
cropland, and disturbed habitats. It occupies mid- to high-elevation sites
in the US Pacific Northwest, where it is best adapted to dry habitats.
It is intolerant of shade. It is not yet known to occur in the province.
It is spreading on rangelands and roadsides in neighbouring Washington
and Idaho.
SPREAD
Plumed seeds are dispersed by wind shortly after maturity. The outer plumeless
seeds remain in the seed head until it disintegrates in the autumn or
winter.
