This is an entry from the blog Dog-Apparel which is from Florida
"The most poisonous plant in Britain to horses is Ragwort. Don’t know if this helps, it is now a "notifyable" (sic) plant and if you see it you are supposed to pull it up."
Ragwort is not a notifiable weed in the UK. There is no such thing in UK law. It is also questionable if it is the most poisonous plant. There are certainly plants that are far far more deadly.
Also you should not pull up ragwort where ever you see it, as this is a criminal offence under the 1981 Wildlife and Countryside Act, unless you have the
owner or occupier of the land's consent. See ragwort is sometimes protected for more details.
There is a common problem with people thinking they are doing good by pulling up ragwort. Living ragwort is ignored by livestock. Dead ragwort is a different matter. By pulling it up an leaving it you may be endangering animals. There is also the problem with other plants which are not ragwort, being misidentified
Ragwort is an ecologically important plant and there are cases where habitats on
nature reserves have been damaged by its removal by well-intentioned but
ignorant individuals, who, like the writer of the Dog-Apparel blog have read something incorrect somewhere and who have just repeated it.
This blog Eco Holidays and Adventures puts the whole thing very succinctly in regards to ragwort with the comment:
So, when you are out exploring the countryside – think of their trees as you would of your garden fence; their plants as you would of your rosebush; their gates as your own front door.
Would you want someone to leave your front door open, break down your fence and snap your rosebush in half?
I didn’t think so…….