Spores of bacterial blight and halo blight can survive inside bean seed and in plant debris in the soil. Seed contamination is an effective means of both local and widespread dissemination of the pathogens. Seedlings arising from infected seed harbor large numbers of bacteria. Both pathogens can survive on alternate weed hosts and volunteer bean plants in the area. The bacteria survives for about 1 year in plant debris.
Survival is generally longer in residue left at or near the soil surface.
High humidity, rain, or both favor rapid development of the disease in the field. Bacterial spores are spread by windblown rain and splashing irrigation water or through contact between adjacent leaves wet from rain or dew. Development of bacterial blight is favored by temperatures in the 85 to 95 degrees F range. Halo blight is considered a cool season disease and is favored by temperatures in the 65 to 75 degrees F range. Use certified disease-free seed.