Pseudomonas syringae pv. phaseolicola Populations and Halo Blight Severity in Beans Grown Alone or Intercropped with Maize in Northern Tanzania. R. B. Mabagala, USDA-ARS and Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. A. W. Saettler (deceased), USDA-ARS and Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Plant Dis. 76:687-692. Accepted for publication 26 February 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0687.

In tests in northern Tanzania, populations of Pseudomonas syringae pv. phaseolicola on and in bean (Phaseolus vulgaris) foliage were higher, severity of halo blight on foliage and pods was greater, and incidence of seed infection was higher when beans were intercropped with maize (Zea mays) than when beans were grown alone. Maize leaves did not support high populations of the pathogen and thus did not seem to provide additional inoculum for the bean crop when the two were grown in association. However, bean leaves in the intercrop system took longer to dry after rainfall and were wetter than those in the monoculture. Simultaneous measurements of parameters related to the pathogen, disease, and weather are therefore needed to understand the effect of a bean/maize intercrop on incidence and severity of disease.