Disease Note

Ashy Stem Blight, a Serious Disease of Cowpea in Botswana. D. W. Burke, Department of Agronomy, Botswana Cowpea Project, Colorado State University, Fort Collins 80523. K. Conniff, P. Ditshipi, and C. J. deMooy, Department of Agronomy, Botswana Cowpea Project, Colorado State University, Fort Collins 80523. Plant Dis. 70:603. Accepted for publication 21 February 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-603e.

Ashy stem blight of cowpea (Vigna unguiculata (L.) Walp. subsp. unguiculata), caused by Macrophomina phaseolina (Tassi) Goid., severely damaged drought-stressed plants in all stages of growth in Botswana, where this disease has not been reported previously. The disease killed plants of certain genotypes but did not infect plants of other genotypes during the 1984–1985 season. The disease, which was most pronounced in plants approaching senescence, occurred in beans (Phaseolus vulgaris L.) but not in Sorghum vulgare Pers., another known host of the fungus, grown in many fields alone or interplanted with cowpea that became infected. This suggests that the strain(s) of M. phaseolina active in the Botswana fields has pathogenic specificity for legumes.