Severity of Spring Black Stem on Alfalfa Cultivars in Ohio. L. H. Rhodes, Associate Professor, Department of Plant Pathology, The Ohio State University and Ohio Agricultural Research and Development Center, Columbus 43210. D. K. Myers, Associate Professor, Department of Agronomy, The Ohio State University and Ohio Agricultural Research and Development Center, Columbus 43210. Plant Dis. 70:746-748. Accepted for publication 28 February 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-746.

Spring black stem (SBS) severity differed among alfalfa cultivars in the field at three locations in Ohio in 1983 and 1984. Of the 10 cultivars represented at all locations, Classic and Vernal had the lowest disease severity rating (DSR). First- and second-harvest yields were negatively correlated with DSR. In a greenhouse study of selected cultivars, dry-matter yields were reduced 20% by artificial inoculation with Phoma medicaginis var. medicaginis, even though plants not subjected to artificial inoculation also became infected. The cultivar Vernal, classed resistant under field conditions, had the highest DSR in the greenhouse. Saranac AR, classed intermediate in the field, had the lowest DSR and no yield reduction resulting from artificial inoculation in the greenhouse.