Of course, we all know that weeds are just plants in the wrong place, but the bright yellow plant which dominates over-grazed fields and roadsides has such a bad reputation that most people regard it as simply disposable.
Numerous web sites advise how to wipe it out, the Highways Agency spends hundreds of thousands of pounds trying to extirpate it and it is the only weed dignified with an Act of its own (the Ragwort Control Act), which specifies how its spread can be controlled, particularly on land used for horses and livestock. It does contain alkaloids which poison animals which eat it, but they won’t normally do so if it is alive (it tastes bitter and the smell crushed is such that the Scots called it ‘Stinking Willy’). Only when it is harvested with grass, when it loses its taste and smell and is easily eaten, does it become a threat.
Even if we could destroy ragwort, it would have major effects on wildlife. At least 30 species of insects and other invertebrates are totally dependent on Ragwort as their food. 52 insects are known to regularly feed on Ragwort as a significant foodplant – it is well know as a food plant for the Cinnabar moth. Trying to eradicate ragwort risks losing other similar plants – St John’s wort, tansy, hawkweeds, and so on – which may have much more fragile populations.