Diplodia citrus rot

Diplodia rot, caused by the fungus Diplodia africana (often associated with Botryodiplodia theobromae), is a destructive plant disease affecting a wide range of citrus species. This pathogen is known for its ability to cause both stem-end rot in fruits and systemic dieback of woody tree parts.

Citrus trees such as lemons, oranges, and grapefruits are highly susceptible to this infection. The fungus primarily invades the host through wounds, pruning cuts, or areas weakened by abiotic stress, such as frost damage, heat stress, or excessive soil moisture which compromises the root system.

The visual symptoms on fruit typically begin as a dark, water-soaked spot at the stem end, which eventually turns black and leathery as the infection spreads. On trees, the pathogen causes branch dieback, where the bark dries, cracks, and may exude gum (gummosis). As the disease progresses, the leaves on affected branches may turn yellow and wither prematurely.

Optimal development for Diplodia africana occurs in tropical and subtropical climates characterized by high temperatures and humidity. The fungus survives unfavorable conditions as pycnidia or mycelium within dead wood, fallen debris, and infected fruits. Spores are then dispersed by splashing water, wind, and movement of equipment during standard agricultural operations.

Managing this disease requires a rigorous integrated approach to maintain tree health and reduce pathogen inoculum levels. Recommended control practices include:

• Regular pruning and removal of all dead or diseased wood.
• Applying protective wound dressings to large pruning cuts.
• Maintaining proper irrigation and fertilization to prevent tree stress.
• Executing preventative fungicide sprays during high-humidity periods to protect fruit and susceptible bark tissues.