Peanut leaf spot (Didymella)

The disease is caused by the ascomycete fungus Didymella arachidicola (anamorph Phoma arachidicola). It is a serious fungal pathogen that manifests as a necrotic leaf spot. The disease impacts the plant's ability to undergo photosynthesis, directly affecting the yield and quality of the peanut crop.

The primary host of this pathogen is the cultivated peanut (Arachis hypogaea). The infection can manifest on various plant structures including foliage, stems, petioles, and stipules. If left unmanaged, the fungus can extend its range to the pegs and pods, rendering the harvest commercially unviable.

Symptoms initially appear as small, scattered brown or black spots on the leaves. As the disease progresses, these spots expand, often surrounded by a chlorotic halo. Mature lesions exhibit dark pycnidia, which serve as the primary source for further spreading. Extensive infection often leads to premature leaf senescence and defoliation.

The development and spread of Didymella arachidicola are heavily influenced by high relative humidity and frequent rainfall. Fungal spores are disseminated by splashing water, wind, and contaminated debris. Warm temperatures significantly accelerate the pathogen's life cycle, making wet seasons particularly dangerous for peanut production.

Integrated disease management (IDM) is essential for minimizing crop losses:

• Implementation of a rigorous crop rotation program.
• Removal and deep burial of infected crop residues to reduce inoculum.
• Use of disease-free, high-quality, and treated seeds.
• Application of broad-spectrum fungicides during early disease stages.
• Monitoring weather patterns to schedule preventative sprayings.