Olive leaf spot

Olive leaf spot, caused by the fungus Spilocaea oleaginea, is the most widespread and damaging disease affecting olive trees globally. This pathogen specifically targets the leaves of the olive tree, disrupting its metabolic processes and significantly impacting the health and longevity of the host plant.

The primary host for this fungus is the olive tree (Olea europaea). The disease manifests primarily on the leaf blades, but it can also affect petioles and sometimes fruit stems under severe infestation conditions, which leads to extensive defoliation and a reduction in photosynthetic capacity.

Symptoms are identified by circular spots on the leaf surface, which start as brown or dark-gray lesions and are often surrounded by a chlorotic yellow halo. These spots are sometimes called "peacock eye" due to their unique appearance. In periods of high humidity, the spots develop a dark, felt-like layer of conidia visible on the leaf's underside.

The development of the disease is heavily dictated by environmental factors, particularly moisture and temperature. Spore germination and infection are most successful at temperatures between 10°C and 20°C when free water is present on the leaves for several hours. Continuous rainfall and high humidity are the primary drivers of the pathogen's spread throughout the canopy.

Management and prevention focus on reducing the inoculum density and improving orchard ventilation. Pruning is essential to allow light and air to penetrate the canopy, which helps keep leaves dry and limits the fungus's ability to infect. Copper-based fungicides are the standard chemical defense, applied preventatively before the onset of favorable weather conditions.

• Regular canopy pruning to enhance air circulation.
• Sanitation by removing and destroying heavily infected leaves.
• Application of copper fungicides during the wet season.
• Monitoring weather patterns to time preventative spray applications.