We are doing battle with yellow starthistle. Acres of our property were covered in it when we bought the place last year. I agree with Frank that 2,4-D (basically, Weed-B-Gone) seems to work much better than Roundup. With yellow starthistle, timing is everything when it comes to spraying. We hate spraying, but there is no other way for us to get rid of it. Put a huge dent in it, and we'll attack it again later in the year, and again in the spring. It's very easy to pull if the soil is damp, but there is no way to do that on a large scale. Was easy enough to pull in the garden though! Putting Preen down afterwards was a huge help. I've had almost none grow back.
