Peanut alternaria leaf spot

Peanut Alternaria leaf spot is a fungal disease affecting peanut crops worldwide, caused by the pathogenic fungus Alternaria arachidis. This pathogen belongs to the group of foliar diseases and is known to significantly impact photosynthetic efficiency in commercial peanut production.

The disease primarily targets the foliage of the peanut plant (Arachis hypogaea). While infection is usually localized to the leaves, severe outbreaks can lead to premature defoliation, where the fungal mycelium affects petioles and stems, ultimately weakening the plant structure.

Clinical symptoms appear as necrotic lesions that begin as small, dark brown spots. As the infection progresses, these spots expand, often developing a characteristic concentric zonation and a dark velvety layer on the surface, which contains the conidia of the fungus.

The proliferation of Alternaria arachidis is heavily dependent on microclimatic conditions. Warm temperatures ranging from 20°C to 28°C combined with high relative humidity and leaf wetness are essential for spore germination and colonization of host tissues.

Economic losses are prevented through integrated pest management (IPM) practices. Key strategies include the removal of crop debris after harvest, practicing crop rotation, selecting tolerant cultivars, and applying systemic or contact fungicides when disease pressure thresholds are reached during the growing season.