Olive peacock spot

Olive peacock spot, caused by the fungus Fusicladium oleagineum (formerly Spilocaea oleaginea), is the most widespread foliar disease of olive trees. The term «semilatent» refers to the pathogen's ability to remain symptomless within the leaf tissue for a considerable duration before visible lesions appear. This makes early detection challenging for farmers.

The causal agent is a fungus that infects leaves primarily through the stomata. Once inside, the mycelium colonizes the sub-cuticular space. The characteristic symptoms manifest as dark, circular spots often ringed with a yellow halo, resembling the eyes on a peacock's tail. These spots are the result of fungal conidiophores emerging through the leaf surface.

The impact of this disease is significant, primarily due to severe defoliation. As leaves drop prematurely, the tree’s photosynthetic capacity is drastically reduced, which leads to stunted growth, weakened branches, and a substantial decrease in fruit yield. Prolonged infections can compromise the tree's health to the point where it becomes vulnerable to secondary pests and environmental stressors.

The spread of the fungus is highly dependent on environmental conditions, particularly high humidity and temperatures between 10°C and 25°C. Rain splash is the primary vector for distributing conidia from infected leaves to healthy ones. The disease cycles rapidly during mild, wet winters and springs, allowing the pathogen to persist within the orchard canopy.

Effective management requires an integrated pest management (IPM) strategy focused on prevention and cultural practices:

• Pruning trees to improve airflow and increase sun penetration within the canopy.
• Sanitation practices, including the removal and destruction of fallen infected leaves.
• Application of copper-based fungicides during the wet season to protect new leaf growth.
• Implementing regular field monitoring to assess infection levels and timing treatments appropriately.