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Pod and Stem Blight (Diaporthe phaseolorum var. sojae)
Johnnie P. Snow
Louisiana State University (retired)
Pod and stem blight occurs in every soybean producing area of the United States. It is a major cause of seed damage, resulting in poor seed quality. This poor seed quality results in grade reductions and lower prices for the producer. The fungus overwinters on seed or on crop residue. Infection can occur early, but it is usually a late season disease, favored by warm humid weather. Disease is more severe if harvesting is delayed.
The most characteristic symptom of this disease is the arrangement of black fruiting structures in linear rows on the stems. Infected seed crack and shrivel and are often covered with white mold. These seed fail to germinate, or produce weak seedlings with brownish-red pinpoint lesions on the cotyledons. Reddish-brown streaks appear on the seedling stem near or below the soil line.
Pod and stem blight is managed by planting pathogen-free seed and foliar application of fungicides from mid-flowering to late pod. Harvesting soybeans promptly at maturity will reduce pod and seed infection.