Runner Beans Yellow, Soft and Dwarfed
 

Up until this week I have been picking a superb crop of runner beans.
But within the last week I am seeing more and more yellow, soft, furry,
dwarfed beans. Can't be for lack of water - we've had more than enough
rain. I've checked and the soil is moist: might be too much water?
Had same problem last year.
Any ideas anyone?
DAvy