Late leaf spot of peanut

Late leaf spot of peanut is a destructive fungal disease caused by the pathogen Phaeoisariopsis personata (also known as Cercosporidium personatum). It is considered one of the most economically significant foliar diseases of peanuts worldwide, capable of reducing yields by up to 50% if left unmanaged.

The primary host for this pathogen is the cultivated peanut (Arachis hypogaea). While the disease primarily impacts the foliage, it can spread to all above-ground parts of the plant, including stems and pegs, leading to severe physiological stress during the crucial phases of pod development and maturation.

Symptoms appear as small, dark brown to black spots on the underside of the leaves. These spots are typically circular and more pronounced than those caused by early leaf spot. Under high humidity, dark sporulation of the fungus becomes visible on the underside of the spots, often appearing as concentric rings that indicate the pathogen's active reproduction.

The development of the disease is strictly dependent on environmental conditions. High humidity, heavy dews, and temperatures ranging from 20°C to 30°C provide the ideal environment for conidia germination and infection. The fungus persists in infested crop residues left on the soil surface, which serve as the primary inoculum source for subsequent crop cycles.

The economic damage stems from severe defoliation, which severely limits photosynthesis and hinders the accumulation of dry matter in the pods. Effective management requires an integrated approach including crop rotation to prevent pathogen buildup, deep plowing to bury infected residues, and the application of protective or systemic fungicides at the onset of symptoms to minimize yield loss.