Broad beans dead flowers!

[SurreySteve]

After my daily inspection of plant on the allotment I have discovered that some of the flowers on my broad bean plants have turned black and died, they weren't like this 2 days ago! Could anyone advise on the cause and treatment if any to prevent the others going down the same road!

Thanks Steve.

[SurreySteve]

[Robert_Brenchley]

They do this when the flower is over. Eventually, you should find beans growing in their place.