United Kingdom 
runner beans leaves are turning black what has caused this
5 May, 2011
Answers
In some parts of the UK it was very cold two nights ago with a frost in some areas so if they are outside then that sounds the most likely cause.
5 May, 2011
We wont be putting our runner beans outside until the end of May.
5 May, 2011
I can't see where you are in britain but from the midlands north there have been patchy frosts that may have caused the problem
5 May, 2011