Pod and stem blight (Diaporthe phaseolorum)

Pod and stem blight: biology

The fungus that causes pod and stem blight overwinters on seed and infected crop residue. It infects soybean plants early in the season when rain splashes spores from residue or from planting infected seeds. Disease development favours warm, wet and humid weather during the pod-filling growth stages.

Yield losses from pod and stem blight can be significant. Losses are dependent on the cultivar’s susceptibility and the weather during maturity. In years where rainy, wet conditions persist from early to mid-season, damage and yield loss will be higher. Yield losses from pod and stem blight result from incomplete seed fill caused by early plant death.

Although plants are infected early in the season, pod and stem blight symptoms do not become apparent until after mid-season. Symptoms on the stems appear as small, black, raised dots or bumps (pycnidia) that are arranged in rows or islands. Fungal spore-bearing structures appear as black specks in linear rows on dead or dying stems and poorly developed pods. The pod blight phase results in poor quality seeds, with mould and seed decay.