Both diseases are carried on the seed and can be spread from plant to plant by rain, hail or wind. In the soil, blight can survive in old, diseased plants for a year or longer. The disease can be severe when rains are frequent during the growing season, or when beans are grown under sprinkler irrigation. The dead areas enlarge rapidly under favorable conditions until they cover most of the leaf, giving the plants a burned appearance. Pod lesions may appear as small, brown, scabby spots.
Diseased seed are a source of infection the next season.
Plant disease-free seed. This is important because all outbreaks of the disease have resulted from planting infected seed. Use a 2 to 3-year crop rotation. The bacteria overwinters in the plant debris from the previous year's crop. The longer beans are kept out of a field that previously produced a diseased crop, the less chance there is of contaminating the newly planted crop.