This is Yellow Starthistle, also known as golden star thistle, yellow cockspur, St. Barnaby’s thistle. At the stage in the photograph it resembles a dandelion. After it has bloomed it takes on the look of little cottonballs. It can grow from a few inches to 3 feet high.
Some invasive species are unwanted because they push out native vegetation. The Yellow Starthistle does that and more…it is also poisonous to horses.
Chemical measures can control the weed. Effective grazing by goats, cattle and sheep can also prove effective. Goats will eat the weed at any stage of the plant’s growth. Insect and fungi treatments have also been implemented. Burning is not effective because of plant’s extensive root system and its seeds are fire resistant.
If you think you have this in your pastures or find it on public land, please a sample to the Harney County Weed Management Agency at 450 N Buena Vista Ave. #10 in the courthouse.