How to Manage Pests
UC Pest Management Guidelines
Pathogen: Pseudomonas syringae pv. phaseolicola
(Reviewed 8/07, updated 8/07)
In this Guideline:
Halo blight symptoms first appear as small, angular, watersoaked spots (almost resembling little pin pricks) on the undersurfaces of leaves. As these spots grow and turn brown, a characteristic light green to yellow halo appears around the spots. This halo is due to the action of a toxin produced by the bacteria and is a diagnostic symptom of the disease. In severe infections the leaves and upper parts of plants turn yellow (chlorotic). On pods, small watersoaked spots, about the size of pin pricks, develop that grow into sunken spots and turn reddish brown. Under favorable conditions, a creamy white ooze may be seen inside these spots (pod symptoms of common and halo blight diseases are virtually indistinguishable). Seed in infected pods may become infected, and appear shriveled, discolored, and/or smaller than normal size.
Halo blight disease occurs worldwide and can cause extensive losses under favorable conditions, which are moderate temperatures (60° to 73°F, 16° to 23°C) and humid moist conditions. Fortunately, such conditions are unusual in California and thus halo blight is uncommon on beans grown in California. Halo blight bacteria can overwinter in infested debris or in association with seed; infested seed is the most important inoculum source.
Control of halo blight is very similar to the control for common bacterial blight. 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 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. Resistant varieties are available and should be used when appropriate.
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