Councils waste millions clearing roadside verges of this stuff every year because of some misplaced concern for the welfare of horses. There is a very low number of horses (if any) killed by ragwort per year and the effort in 'eradicating' ragwort is wasted. You cant eradicate ragwort: it's a natural part of the English countryside and rather pretty.
a) This act causes a substantial waste of money.
b) is ineffective (just look at the amount of ragwort round motorway verges and generally scattered around)