Late leaf spot of peanut

Cercosporidium personatum (synonym Passalora personata) is a significant fungal pathogen within the Kingdom Fungi that causes late leaf spot in peanuts (Arachis hypogaea). As a specialized parasite, it targets the leaf tissue, leading to severe defoliation and hindering the plant's ability to produce high-quality pods.

The characteristic symptoms include dark brown to black circular lesions on the underside of the leaves. These spots are typically darker and more localized compared to early leaf spot (Cercospora arachidicola). As the disease progresses, these lesions coalesce, leading to rapid chlorosis and significant leaf shedding, which undermines the vitality of the plant.

The fungus overwinters in the soil on infected plant debris, using it as a primary reservoir for the next growing season. Dissemination of the pathogen occurs primarily through wind-borne conidia and splash dispersal during rainfall or irrigation. The development of the fungus is favored by long periods of leaf wetness and warm temperatures, making high-humidity environments particularly dangerous for peanut production.

The economic impact of this pathogen is profound, often resulting in significant yield losses, ranging from 20% to over 50% in untreated fields. Besides reducing pod production, it negatively affects the quality of the kernels, their size, and their oil content, which leads to substantial financial losses for farmers in affected regions.

Effective management strategies require an integrated approach including resistant cultivars, crop rotation, and precise cultural practices. The destruction of crop residues through deep plowing is essential to reduce the inoculum level. Additionally, chemical control via the application of specialized fungicides is crucial, especially when weather conditions are conducive to rapid fungal spread.