Citrus Melanose

Citrus melanose, caused by the fungus Diaporthe citri (the anamorphic stage is Phomopsis citri), is a significant fungal disease impacting citrus production globally. The disease targets various parts of the tree, primarily affecting the aesthetics and marketability of fruit while causing physiological stress to the canopy.

The host range of Diaporthe citri includes most commercially grown citrus species, such as lemons, oranges, grapefruits, and tangerines. The pathogen is most aggressive toward young, developing tissues. While the disease can manifest on leaves and twigs, the most economically devastating impact occurs when young fruit surfaces are colonized during their early growth stages.

Symptoms of melanose typically appear as small, dark brown to black raised spots that feel rough to the touch, resembling sandpaper. As the fruit matures, these spots may merge into larger, hardened, scab-like areas. Severe infections can lead to fruit distortion, premature dropping, and, in cases of severe leaf infestation, reduced overall plant vigor due to necrosis.

Development and spread of the pathogen are highly dependent on moisture. Spores are produced within pycnidia located on dead twigs and branches, then dispersed by splashing water or heavy dew. Extended periods of rain or high humidity during the critical fruit-set window create the ideal conditions for infection to take hold and proliferate throughout the orchard.

Integrated disease management for citrus melanose relies on both cultural and chemical control measures:

• Rigorous pruning to remove all dead wood and twigs where the fungus overwinters.
• Applying copper-based fungicides during the early fruit development stage to protect sensitive tissue.
• Maintaining optimal tree spacing and pruning practices to improve air circulation and reduce humidity within the canopy.
• Sanitation measures to prevent the buildup of inoculum within the grove.