Knapweed - a bane for ranchers.
Spotted and diffuse knapweed showed up here in central Colorado about 1975. It likes sandy or gravel soil and is just plain hell to get rid of. One of our neighbors never sprayed. They had both cattle and horses on thier place.
By summer, the knapweed is 2 -3 feet high and in full bloom. After it blooms, the stems are hard and cattle won't touch it.
After 15 years of work, I have finally gotten rid of it. I put up a woven wire fence to keep the neighbors weeds out and walked almost daily around the place, especially near shrubs chopping weeds with a hoe or hand spraying. But I won. (Forgot to mention the neighbors got foreclosed on and are gone,)
Two years ago, after foreclosure, the buyer had the property sprayed. I don't know what they used, but their knapweed is gone!!
Even when cattle eat knapweed in the rosette stage, the plant will still bloom and make seeds - just not as tall.
Canadian thistle is loved by cattle. We had some CRP land infested with Canadian thistle. We took about 40 acres out of CRP and grazed it. Thistle is gone. Cattle will eventually kill it out.
CP