Cercospora is caused by the fungal pathogen Cercospora zonata. This disease can cause problems in some years. The disease often occurs when plants are growing in wet patches, particularly where free water remains on the soil surface.
What to look for
Dark irregular lesions which may be difficult to distinguish from ascochyta blight, however, lesions of cercospora tend to be darker and their shape is more irregular. Within the spots a concentric ring pattern can often be seen.
This disease has not been well studied. Cercospora is thought to survive on bean trash and its spores are probably spread by rainsplash. It is not known to be seedborne.
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