Peanut cercospora leaf spot

The fungus Cercospora arachidicola is the causative agent of early leaf spot in peanuts (Arachis hypogaea). It is a major fungal pathogen that severely affects the foliage of the plant, significantly reducing its photosynthetic capacity. The pathogen survives between growing seasons on infested peanut residues left on the soil surface, providing a primary inoculum source for new crops.

Peanut plants are the primary host for this fungus. The disease primarily attacks the leaves but can also infect stems and petioles under favorable conditions. Once established, the pathogen weakens the plant's structural integrity and physiological functions, leading to premature senescence and a drastic reduction in biomass production during the pod-filling phase.

Symptoms typically manifest as small, circular spots on leaves that are brown to dark brown, surrounded by a distinct chlorotic or yellow halo. As the infection progresses, the number of spots increases, often causing the leaves to wither and drop prematurely. In humid conditions, a fuzzy, gray appearance may be observed on the underside of the leaves due to conidia production.

Environmental conditions are critical for disease development. High relative humidity, frequent leaf wetness, and temperatures between 20°C and 30°C create the perfect environment for spore germination and colonization. Wind-borne dispersal and rain splashing are the primary methods of transmission throughout the field, often causing rapid spread within dense canopies.

Economic damage from Cercospora leaf spot is primarily driven by yield loss, which can reach 50% if left unmanaged. Control strategies rely on integrated pest management (IPM) practices, including:

• Applying preventative or curative fungicides.
• Implementing crop rotation to break the pathogen's life cycle.
• Using certified seeds and resistant cultivars.
• Managing irrigation to avoid prolonged leaf wetness periods.
• Removing or burying crop residues post-harvest.