Alternaria leaf spot of cotton

The causal agent of Alternaria leaf spot is the fungus Alternaria gossypii. This fungal pathogen is a significant threat to cotton production worldwide, causing extensive foliar damage and reduction in the quality and quantity of the harvested lint and seed.

The primary host for this fungus is the cotton plant (Gossypium species). The disease affects all aerial parts of the plant, including cotyledons, true leaves, stems, and the developing bolls, which often leads to substantial yield losses in affected fields.

Initial symptoms present as small, circular, reddish-brown spots on the leaves. As the infection progresses, these spots expand, often showing concentric rings or zones. Severe infections cause the foliage to yellow, wither, and drop prematurely, leading to reduced photosynthetic capacity.

The development of the disease is favored by warm, humid conditions, especially during periods of heavy rainfall or prolonged dew. Fungal spores (conidia) are dispersed primarily by wind and splashing water, allowing the disease to spread rapidly through a cotton field.

Management strategies focus on integrated pest management practices to suppress the pathogen. Prevention is key, including the use of disease-free seeds and the destruction of crop residues. Chemical control using registered fungicides is often necessary during the early stages of infection to prevent epidemic outbreaks.