Alternaria leaf spot of cotton

The disease is caused by the fungus Alternaria macrospora, which is a significant pathogen responsible for leaf spot in cotton. This fungus is widely recognized for its ability to cause severe premature defoliation in commercial cotton plantings.

The primary host for this fungus is the cotton plant (Gossypium spp.). While it primarily targets the foliage, the infection can also extend to the bracts and cotton bolls, potentially damaging the overall crop structure and yield capacity.

Symptoms typically manifest as small, brown, circular spots that eventually expand into larger, irregularly shaped lesions with distinct concentric zones. In humid environments, a dark olive-brown mold, representing the pathogen's conidia, is clearly visible on the surface of the spots.

The development of Alternaria macrospora is highly dependent on environmental conditions, particularly high humidity, frequent rainfall, and warm temperatures. The spores are primarily wind-dispersed, allowing the disease to spread rapidly across large fields during the active growing season.

The economic impact is significant due to the loss of photosynthetic leaf area, which hinders boll development. Severe infections lead to premature shedding of leaves and fruit, resulting in yield losses and reduced fiber quality, which can devastate plantation profitability.

Effective management strategies include:

• Strict field sanitation to remove and destroy infested crop debris after harvest.
• Crop rotation to reduce primary inoculum levels in the soil.
• Use of resistant cotton varieties tailored for specific regions.
• Timely application of fungicides during the growing season to prevent secondary spread and protect the canopy.