Sweet orange scab

Sweet orange scab is a fungal disease caused by the pathogen Elsinoe australis. It affects a wide range of plants belonging to the Citrus genus, including sweet oranges and other citrus varieties. The disease is primarily a cosmetic issue that significantly diminishes the market value of the fruit, making it unsuitable for fresh export.

The fungus overwinters in infected plant tissues, such as fallen leaves, twigs, and fruit lesions. When conditions become favorable—specifically during periods of high humidity and rainfall—the fungus produces spores (conidia). These spores are then dispersed throughout the orchard via wind splashes or irrigation, infecting new succulent tissues of the citrus trees.

The characteristic symptoms of the disease include the formation of raised, corky, or wart-like growths on the surface of leaves, twigs, and fruit. These lesions are typically small at first but can enlarge and merge, covering a significant portion of the fruit peel. Severe infections lead to the deformation of the fruit, causing it to become stunted and often triggering premature drop.

Development and spread of sweet orange scab are highly dependent on environmental factors. The pathogen thrives in regions with frequent rain, high humidity, and moderate temperatures. The most susceptible stages of plant development are during the growth of young leaves and the early stages of fruit set, where the tissues are soft and easily penetrated by the fungal mycelium.

Effective management requires an integrated approach to minimize the impact of the disease. Key strategies include:

• Maintaining good orchard sanitation by removing and destroying all infected plant material.
• Pruning trees to improve air circulation within the canopy, which helps keep tissues drier.
• Applying protective copper-based fungicides during key growth stages, particularly shortly after flowering, to prevent infection on young, developing fruit.