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Stem canker


Photo by Craig Grau, University of Wisconsin

Pathogen(s) causing disease:

Diaporthe phaseolorum var. caulivora

Symptoms:

Enlarging cankers that are reddish brown to black, slightly sunken, and girdling develop on the lower part of the stem, causing the plants to wilt, wither and die because the flow of water and nutrients to the foliage is reduced or stopped completely. The lesions usually occur at the fourth or fifth node (joint) or in the region of the second and third trifoliate leaves. Infected stems are brittle, and the plants break over easily at the center.

Conditions:

A daily mean temperature of 70 F (21 C) during prolonged wet weather early in the season is optimum for disease development.

Management:


Photo by Craig Grau, University of Wisconsin
Plant high-quality, certified seed that is disease-free and will germinate more than 80 to 85 per cent in a warm germination test or over 70 per cent in a cold germination test. Plant thoroughly cleaned seed in a warm, fertile, well-prepared seedbed. Treat with a protective seed-applied fungicide. Bury infected crop residue after harvest, where soil erosion is not a problem. Where feasible, rotate soybeans for 1 or 2 years with corn, sorghum, small grains, alfalfa, or forage legumes. Make a foliar application of a labeled fungicide. This is suggested for seed-production fields. Spraying increases seed size, quality, and germination. The proper and timely application of a fungicide not only controls stem canker, but also pod and stem blight, Septoria brown spot, anthracnose, Cercospora leaf spot or blight, target spot, and purple seed stain. Harvest as soon as the crop is mature. When harvest is delayed under wet conditions, seeds may be infected throughout the plant.

Sources:

U of IL
ISU

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