We have a problem with ragwort which we control by pulling but this year we are going to have to spray. If you have ragwort in the amount I think you are saying you will never get rid by pulling. Each plant can produce ten thousand seeds and each seed can lay dormant for ten years, as said by my agri advice office. Sheep eat the young growth and have no problems but it is at its most poisonous when it is dried such as in hay, its sugars concentate then and make it sweet rather than bitter when green and left by animals. Each section of root left can grow into another plant. If sheep are continually in a field they keep the ragwort down but as soon as they are off it will take over again. Lambs can succumb to ragwort but older sheep are OK. Best spray to get shut if you have cattle as well.