I pulled it all up by the roots every year before it went to seed. It was a pain, but not too bad because it's not very deeply rooted. I tried round up on the small ones, but it wasn't very effective.
Thank you! I had that growing in my pasture and could not identify it. It started as just a handful of plants and the chickens loved it, so I let it be. Then it spread very rapidly and it had to go. It took me three years of pulling, digging and spraying to finally be rid of that stuff. 😒...