Bacterial brown spot of bean

Bacterial brown spot of bean is the most economically significant disease of processing beans in the north-central region of the United States. It also occurs in other bean-growing areas of the United States and the world. The bacterium can on plant debris for 1 year.

Bean
Small 3-9mm (⅛-⅜in), oval, necrotic lesions are apparent on leaves. A narrow yellow-green zone of tissue may be seen surrounding the lesions. Bacterial exudate (ooze) and water-soaking are rarely observed prior to necrosis. The leaf tissue around the lesion may be puckered. Lesions coalesce and their centres fall out, giving leaves a tattered appearance.

On pods, dark brown lesions are generally small, 1-3mm (less than ⅛in) in diameter, necrotic and cause pod malformation by inciting cessation of growth by nearby tissue.

Control
Spray weekly with copper-containing chemicals after symptoms have been observed, particularly when weather is overcast, cloudy and humid and especially when these conditions follow rain or irrigation.

Prevention
Resistant varieties of beans are available. Crop rotation should be practiced.