Soybean stem canker (Phomopsis)

The fungus Diaporthe caulivora is the causative agent of a serious disease in soybeans, widely known for its ability to cause stem canker and significant yield losses. This pathogen thrives in various climatic zones, targeting the vascular system of the host plant and disrupting nutrient transport.

Soybean is the primary host for this pathogen. The fungus persists in infested crop residues, infected seeds, and the soil. It is a persistent pathogen, meaning that once the field is contaminated, the risk of outbreaks remains high in subsequent seasons if proper management practices are not implemented.

Symptoms typically appear as brown lesions near the leaf petioles, which expand to create girdling cankers on the stems. These cankers block the flow of water and nutrients, resulting in the wilting and eventual death of the plant. A hallmark sign is the formation of small, dark fruiting bodies known as pycnidia on the stem surface.

Environmental conditions play a crucial role in disease development. High humidity, frequent rainfall, and temperatures around 20–25°C create the perfect environment for the fungus to spread. Spores are primarily dispersed through rain splashes and wind, infecting plants during the active vegetative and reproductive stages.

Integrated management is essential for control. This includes crop rotation to break the disease cycle, planting certified disease-free seeds, and the application of systemic fungicides at critical growth stages. Deep tillage to bury crop residues can also significantly reduce the initial inoculum level in the soil.

Farmers are advised to monitor fields regularly, especially during flowering, for any signs of discolored stem patches. Early intervention with appropriate fungicides is often necessary to prevent large-scale infections and ensure the viability of the seed crop at harvest.