How to Manage Pests
UC Pest Management Guidelines
Common Bacterial Blight
Pathogen: Xanthomonas campestris pv. phaseoli
(Reviewed 8/07, updated 8/07)
In this Guideline:
Symptoms of common bacterial blight first appear on leaves as small, watersoaked spots and/or light green areas. These spots enlarge and the tissue in the centers dies and turns brown. These irregularly shaped spots are bordered by a lemon yellow ring, which is a diagnostic symptom of common blight. These spots or lesions can develop on the edges or in interveinal areas of leaves. The spots may grow together, resulting in the death of the entire leaf and defoliation of the plant. Infected pods will first show small, watersoaked spots that develop into large, dark red irregular spots. Under favorable conditions, these spots may show a yellow slimy ooze (pod symptoms of common and halo blight diseases are virtually indistinguishable). Seed in infected pods can become infected; white-colored seed may show butter yellow spots when infected. Heavily infected seed may be shriveled and germinate poorly.
Like most bacterial diseases, common bacterial blight is favored by conditions of high moisture and humidity. Because of dry summers, this disease is uncommon in California. Although common blight bacteria can overwinter in infected debris, survival and dissemination in association with seed is more important. In fact, bean seed is produced in California because environmental conditions are unfavorable for development of bacterial diseases.
Plant certified seed produced in arid regions unfavorable for development of bacterial diseases, such as California and Idaho. Avoid the use of sprinkler irrigation, which can provide the needed moisture and humidity for common bacterial blight development in California. In fields known to have had common blight problems, practice a 2 to 3 year rotation and deep plow infested debris. There are no commercially available resistant varieties, although some tolerant cultivars are available (e.g., Great Northern Harris). Bactericides or antibiotic sprays are generally not effective for controlling common blight.
UC IPM Pest Management Guidelines:
R. M. Davis, Plant Pathology, UC Davis
Acknowledgment for contributions to Abiotic Disorders:A. E. Hall, Botany and Plant Sciences, UC Riverside
Acknowledgment for contributions to Diseases/Abiotic Disorders:S. R. Temple, Plant Sciences, UC Davis
Acknowledgment for contributions to Diseases (viruses):R. L. Gilbertson, Plant Pathology, UC Davis