Phytophthora pod rot

Phytophthora megakarya is an oomycete pathogen responsible for the devastating black pod rot of cocoa. It is identified as the most aggressive species of the Phytophthora genus affecting cacao plantations in West and Central Africa, causing significant economic losses to the chocolate industry.

The primary host for this pathogen is the cacao tree (Theobroma cacao). While the disease is most famously associated with the rot of the pods, it also aggressively attacks the trunk and branches of the tree, causing systemic cankers that can eventually kill the entire plant if left untreated.

Symptoms of the disease initially appear as small, translucent, water-soaked spots on the pod surface. These spots rapidly turn dark brown or black, eventually covering the entire pod. Under high humidity, a characteristic white, powdery layer of sporangia emerges on the surface of the lesions.

The spread of the pathogen is driven by environmental conditions, particularly high rainfall and humidity levels between 20°C and 25°C. Rain splashes facilitate the movement of motile zoospores from the soil or trunk to the pods, making the peak rainy season the period of maximum infection pressure.

Effective management requires an integrated approach to mitigate the damage caused by Phytophthora megakarya. Key strategies include:

• Frequent harvesting and safe disposal of infected pods to reduce the inoculum load.
• Pruning trees to improve airflow and reduce humidity levels within the canopy.
• Application of copper-based fungicides at the onset of the rainy season.
• Maintaining optimal orchard hygiene to limit the build-up of the pathogen in the soil.