Two widespread bacterial blights on beans are common blight (caused by Xanthomonas phaseoli) and halo blight (caused by Pseudomonas phaseolicola). These bacteria attack all kinds of beans. Common blight is more severe in warm, moist weather; halo blight is favored by cool temperatures. The bacteria are usually introduced into a garden on infected seed, and can live on infected plant debris in the soil for as long as 2 years. They are spread by rain, splashing water, and contaminated tools. The bacteria multiply rapidly in humid weather. If the water-conducting tissue is invaded, bacteria and dead cells eventually clog the veins, causing leaf discoloration. Often bacteria ooze from infected spots in a yellow or cream-colored mass.
There are no chemical controls for bacterial blights. Avoid overhead watering. Do not work with the beans when the plants are wet. Do not plant beans in the same area more often than every third year. Purchase new seed each year from a reputable company.
Plant Care for Beans