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Effects of Cultivar, Tillage, and Cropping System on Infection of Soybean by Diaporthe phaseolorum var. caulivora and Southern Stem Canker Symptom Development. Craig S. Rothrock, Department of Plant Pathology, University of Georgia, Georgia Experiment Station, Experiment 30212; Daniel V. Phillips, and Thomas W. Hobbs. Department of Plant Pathology, University of Georgia, Georgia Experiment Station, Experiment 30212. Phytopathology 78:266-270. Accepted for publication 19 June 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-266.

The influence of cultivar, tillage, and cropping system on infection of soybean plants by Diaporthe phaseolorum var. caulivora and on incidence and severity of southern stem canker was examined. Three weeks after planting, 34% of all the plants were infected in 1985 compared with 4% in 1986. The percentage of plants infected increased throughout the growing season in both years and was lower under conventional tillage than under no tillage. Infection levels were similar for the two cultivars, but symptom expression was much more severe for Hutton than Coker 368. Disease incidence and severity for the susceptible cultivar Hutton were significantly lower for conventional tillage than no tillage in 1985 and 1986. Smaller but significant reductions in disease were found for Coker 368 under conventional tillage in both years. Although tillage did not significantly affect yield for the moderately resistant cultivar Coker 368 in 1985, the susceptible cultivar Hutton yielded 47% more under conventional tillage than no tillage. Lower infection and disease severity in 1986 resulted in similar yield by these two cultivars under the different tillage practices. Disease incidence and severity in 1985 for Coker 368 and disease incidence and severity for Hutton in 1986 were slightly greater under soybean/wheat double-cropping compared with a soybean/fallow cropping system.

Additional keywords: conservation tillage, Glycine max.