This is bacterial blight of beans. There are three bacteria that can cause it, and the bacteria can be transmitted through the seed. Copper-based fungicides can provide control. Contact your local Cooperative Extension office for fungicide recommendations. Do not save bean seed from year to year, and be sure to practice crop rotation. For more detailed information on the various bacterial blights on beans and photos, visit: Beans-Bacterial Blights.
You can also visit the eXtension web site: Vegetables Problems for diagnosis and management techniques.
