There are three different bacterial diseases in snap beans; brown spot, common blight and halo blight.
Under field conditions, it is often difficult to distinguish between the three. They all typically begin as small, water-soaked lesions on the underside of the leaves. Occasionally a bright yellow spot on the upper leaf surface may be the first sign of infection. As the disease progresses the lesions expand and coalesce to form large, chocolate brown dry areas between the main veins of the leaf. A thin yellow border often (but not always) surrounds affected areas.