Without a laboratory test I would say it is anthracnose. Anthracnose is often present on the seed and that is where the initial infection generally originates. It does overwinter and can be in your soil or compost. Where did you get the seed? Is it some you saved, received from a friend or did you buy it? Bought seed is usually tested for diseases but saved seed is not since many gardeners are not aware of the disease danger that can go with the seed. How the beans got it in the first place will only help prevent it in future years, what to do about it once you have it is your current concern.Unfortunately there is very little that can be done since sprays will not eliminate it. Applications of copper, sulfur and Serenade may reduce the infection level and they are all organic. From a cultural standpoint, do not overhead irrigate, keep the leaves dry. Do not walk in the garden when the plants are wet, even from dew. DO NOT COMPOST THESE PLANTS FOR USE IN YOUR GARDEN NEXT YEAR. DO NOT SAVE THE SEED!

Dry weather will also help. Go to :
http://www.extension.umn.edu/garden/yard-garden/vegetables/anthracanose-and-rust-of-garden-beans/