This fungal disease occurs all over North America and can attack a wide variety of plants such as beans, lettuce, and members of the cabbage family. Symptoms on beans begin as water-soaked spots on blossoms, stems, leaves, and pods that enlarge rapidly and become covered with a cottony white mold. Infected leaves wilt, yellow, and die. Infected pods may rot. The fungus overwinters in plant residues in the soil.
Destroy diseased plants as soon as you notice them. Don't wet tops of plants while watering, or water early in the day so plants are dry before nightfall. Use a 3- to 4-year crop rotation with nonsusceptible plants such as corn, beets, or spinach. To prevent infections, spray with an approved fungicide just as buds open and again a week later.
Photo courtesy of Howard F. Schwartz, Colorado State University, Bugwood.org