Leaves develop small watery spots, which enlarge, discolour to brown and may kill off foilage over time. When weather cools, narrow green or yellow bands may border the spots and leaves may turn yellow or brown rapidly and die off. Occasionally stems develop long reddish areas and a tan or yellow ooze will emerge from the spots. Typically it is first introduced to the garden through infected seeds and spread by splashing water, rain and tools. It multiplies rapidly in humid weather invading water-conducting tissue and clogging the veins, which causes the discoloration.
Bacterial blight can live on debris and infected seeds for up to two years.
Avoid working in the garden when plants are wet to avoid spread by contact and avoid its initial occurrence by buying reputable seeds from a known company. Purchase new seeds each year. Once an area has been infected, reinfections can occur for up to 3 years, so it is best to plant beans in a new site each year. Unfortunately, there are no chemical controls for bacterial blight. Could be leaf blight.