Solved Mystery plant - wild flower perhaps?

This was causing me confusion at first...Ragwort...Ragweed very different plants...but both in Asteraceae

Quote wiki....

"Ambrosia artemisiifolia, with the common names common ragweed, annual ragweed, and low ragweed"

and

"Jacobaea vulgaris, syn. Senecio jacobaea
Common names include ragwort, common ragwort,[4] stinking willie,[5] tansy ragwort, benweed, St. James-wort, stinking nanny/ninny/willy, staggerwort, dog standard, cankerwort, stammerwort. In the western United States it is generally known as tansy ragwort, or tansy."

Both plants seem to be a major problem.
Both should be weeded out.

Cinnamon is quite correct..Ragweed allergy is a major public health concern....see

Modifiable Risk Factors for Common Ragweed (Ambrosia artemisiifolia) Allergy and Disease in Children: A Case-Control Study. - PubMed - NCBI

 

Ragwort below....





Surprisingly this is the national flower of the Isle of Man. Illegal to let it grow there but it can be seen in abundance all over the island.

 

Ragweed (Ambrosia artemisiifolia) is the one the French were alerted about. It's wind pollinated, and as Silver Surfer says, the pollen causes some people an extreme allergic reaction. I nicked a copy of the poster about ragweed, which I've still got somewhere.
I was in the Drome departement in the SE of France, where they've allowed rivers to 'naturalise' and reintroduced beavers. I was a research assistant for a PhD student quite randomly at the nature reserve featured in this article I've just googled about ragweed (In French):

lutte contre l'ambroisie Ambrosia artemisiifolia L

Ragweed was spreading in disturbed ground e.g. in the flood plain of the river. Lovely place with fields of sunflowers, stone martens living in the roof of the old unrestored farmhouse
where we stayed and gorgeous traditional villages that'd clearly benefited from exporting their men in French colonial times.

I think ragwort is more of a problem for horse owners.