I had two established ones and tried to dig them out. What a job! They go really deep and its impossible to get it all out. The "roots" are like a white tuber and any bits that break off regrow. So, I dug out as much as I could, then waited a year. When any new shoot comes up, give it chance to get about 4 inches tall or so, then spray with systemic weed killer (Roundup for eg,). This soon clears the problem. Just keep a look out when you pass for any more and spray em! After two years they are no more.....RIP Yukka's :o)