Hi Tevor and welcome to GoY the lower leaves on the runner beans will start to die off once the beans have set. Make sure you keep picking them, if you don't the plant has done its job and set seed then it dies.

I wish it was as simple as that. I am picking every day and this problem started within a week or so of early harvesting. First signs are that some leaves up one stem start to go limp, curl and brown at the edges. Progressively other leaves are affected and eventually the stem itself starts to brown and will die completely if I don't cut it out beforehand. At this time I probably have about 50% plants completely healthy and the rest in various stages of decay. I still have masses of flowers and beans growing on the healthy stems and limp leaves and small beans on the infected plants.

If it is a virus or bacterial problem in the earth/compost,. then identification might help me stop it next year.

Any further help/suggestions would be appreciated.

Send a PM to ian digs he knows more about runner beans than me.