Mold on beans is caused by 2 related fungi. One fungus, Sclerotinia sclerotiorum, is responsible for white mold, also known as watery soft rot. The white mold fungus forms dark, seedlike structures that can drop to the soil and survive through adverse conditions to infect bean crops for the next few years. The fungus Botrytis cinerea is responsible for gray mold. This fungus produces tan to gray-brown fungal strands. Both fungi often attack weak or dead plant parts, such as old blossoms. Once established on a plant, these diseases can be spread to healthy plants by wind or splashing water, or when infected plant parts touch healthy ones. Mold spreads quickly in cool, wet weather.
Remove and destroy all diseased plants as soon as symptoms appear. Water healthy plants early in the day. Avoid wetting plant foliage. Do not plant beans in the affected area for 3 to 4 years. Until then, plant other resistant vegetables such as corn, beets, Swiss chard, or spinach. Always plant beans in well-drained soil, and avoid overcrowding to improve air flow. Spray the foliage with a fungicide containing chlorothalonil.
Plant Care for Beans