Yellow star thistle is one of the most opportunistic weeds that will invade your domain. It will come onto your property in the mechanism of earth moving equipment and is often the first thing that will grow after earthwork. It also will arrive in the hoofs of cattle and has spread over much of the public and private grazing land in the west. It can be eradicated from smaller areas like yards by hand pulling, I have rid several areas with a consistent year around weeding program, targeting the plant just before flowering. There is research against the spread of this noxious weed as it is choking many Bay Area communities.