Squarrose knapweed, introduced from southwest Asia and the Middle East, became weedy in northern California and Utah by the early 1950s. How it
was originally introduced is not known, but its spread in California
and Utah was associated with the trailing of range sheep. Squarrose knapweed grows in the Klamath,...
Yellow starthistle (Centaurea solstitialis L.) is a member of the knapweed
(Centaurea L.) complex. It is poor forage for all livestock and causes
“chewing disease,” a nervous disorder, in horses. Yellow starthistle infests
millions of acres in California and the Pacific Northwest. Infestations range
from scattered plants to dense stands...
Four species of Centaurea are commonly found in central and
eastern Oregon, including spotted knapweed (Centaurea
maculosa), diffuse knapweed (Centaurea diffusa), Russian
knapweed (Centaurea repens), and yellow starthistle
(Centaurea solstitialis). These four species are a serious problem
throughout Oregon and the Pacific Northwest. Stands of knapweed can choke out natural...
Knapweeds are a serious problem in Oregon because they vigorously
invade disturbed or degraded sites and form dense populations that exclude native and desirable plant communities, causing economic and
ecological losses. Their ability to spread rapidly by seeds and
roots makes control very difficult. Seeds can remain viable for 5...
In the heat of summer in the Rogue Valley, yellow starthistle (Centaurea solstitialis) raises heads of brilliant yellow flowers rigidly defended by sharp spines. Although bees reap double benefits of nectar and pollen during a season when most native plants no longer are flowering, this nonnative weed is a threat...
Centaurea solstitialis L. (yellow starthistle) and C. × moncktonii Britt. (meadow knapweed) are members of the genus Centaurea in the Asteraceae family. Both species have become serious management concerns as invasive species in North America, often displacing native vegetation and costing land managers millions of dollars to eradicate. Seven plants...