Citrus scab

Citrus scab is a fungal disease caused by the pathogen Sphaceloma fawcettii (syn. Elsinoë fawcettii). This fungus primarily affects the aerial parts of citrus trees, causing disfigurement and affecting the overall quality of the fruit. As a significant agricultural threat, it necessitates careful monitoring and management to prevent severe economic impact.

A wide variety of citrus species are susceptible to this pathogen, including lemons, grapefruits, mandarins, and certain types of limes. Young plants, particularly those in nursery settings, are highly vulnerable. The disease preferentially attacks young, succulent tissue, such as developing leaves, shoots, and fruit, which are actively growing during the spring months.

Symptoms appear as small, water-soaked spots that eventually develop into raised, corky, wart-like lesions. These lesions can vary in color from light brown to grey. On the fruit, the damage causes severe distortion and the formation of rough, scab-like patches. In severe cases, premature leaf drop and the dieback of tender twigs can occur, significantly reducing the vigor of the plant.

The development and spread of Sphaceloma fawcettii are strictly dependent on environmental conditions, particularly high humidity and the presence of moisture. Rain splashes and wind-borne water droplets effectively disseminate the fungal spores throughout the canopy. Moist weather during the spring flush is the most critical period for disease initiation and rapid spread.

Effective control measures include:

• Application of copper-based fungicides during the early stages of flush and fruit set.
• Sanitary pruning to remove diseased branches and reduce the source of inoculum.
• Ensuring proper spacing and pruning to improve air circulation within the tree canopy.
• Implementing strict quarantine measures when introducing new plant material to prevent the spread of the fungus.