The spots are surrounded by yellow rings on some bean varieties. If the leaves are severely covered, they fall off. In late season, spots may darken as the black over wintering spores are produced. Plow debris under right after harvest. Resistance is available for this disease, although there are many races of the fungus.
Many varieties are resistant to a few races, but few varieties are resistant to most races.
See current recommendations for chemical control measures. Sherf, A.F. and A. A. MacNab. Vegetable Disease and Their Control . John Wiley and Sons, New York. Stavely, J.R. Rust. pp.