Phomopsis Seed Rot, Pod and Stem Blight
Phomopsis longicolla, part of a species complex
Symptoms and Signs:
- white, chalky textured seeds
- mycelium and pycnidia visible on seed surface
- seedlings may have reddish lesions on stem
Pod and Stem Blight
- small, raised black specks (pycnidia) in parallel lines on stem
- Overwinters as pycnidia on plant residue.
- Spores are splashed by rain onto soybean plants in the spring.
- Stems and pods become infected and symptoms start to develop. Most often, infection occurs after prolonged wet periods after flowering and pod set. Seed infection will increase if harvest is delayed in warm, wet weather.
- Do not plant infected seed. Germination of infected seed will be low and plants sprouting from infected seed may develop cankers or experience post-emergence damping-off.
Host resistance: Planting resistant varieties is the most economical approach to disease management. Varieties with resistance to this disease will provide a higher germination rate and decreased symptom development when compared with susceptible varieties.
Cultural practices: Cultural practices like using quality seed, harvesting seed at certain moisture levels, rotating crops, and using tillage can be great additions to a disease management plan. Plant high-quality seed with at least 80% germination or better. A seed treatment is recommended to improve germination of seeds with a 70-80% germination rate. Harvest seed when moisture reaches 13-16%. Delaying harvest can result in higher disease occurrence. Rotating with non-hosts like wheat or corn reduces survival of the fungus. Tillage will also help reduce viable inoculum in the field by burying infective plant debris.
Chemical applications: Fungicides applied to pods at mid-flowering to late pod stage may reduce incidence of Phomopsis seed rot, however yield is rarely increased. This would only be economical for seed of food grad producers. Consult a local extension educator or the soybean disease website for fungicide recommendations.