Olive yellow

Olive yellow is a dangerous systemic plant disease caused by specialized intracellular microorganisms known as phytoplasmas (Candidatus Phytoplasma oleae). This disease belongs to the group of phytoplasmoses, which attack the plant's vascular system, disrupting nutrient transport and causing severe metabolic disturbances within the tree tissues.

The primary crop affected by this pathogen is the European olive (Olea europaea). The disease has significant economic impact in Mediterranean regions, as it leads to the gradual degradation of groves, reduced fruit yields, and the eventual death of the trees if proper phytosanitary measures are not implemented.

The initial symptoms of infection include yellowing and chlorosis of the leaves, which gradually spread throughout the canopy. A characteristic sign also includes abnormal shoot development: internodes become shortened, leading to the formation of "witch's brooms" or dense bushy clusters, while the leaves themselves become stunted and deformed.

The pathogen is transmitted naturally primarily by insect vectors, such as leafhoppers, which feed on the sap of infected trees. Additionally, the infection can be spread through contaminated propagation material during grafting or the use of infected rootstocks, making strict control of nurseries a critical component of disease prevention.

Effective management and protection strategies rely on rigorous adherence to quarantine regulations. Essential control methods include:

• Using only certified, disease-free planting material.
• Removal and destruction of infected trees along with the sterilization of pruning tools.
• Controlling insect vector populations through systematic insecticide applications.
• Regular field monitoring to detect and isolate symptomatic trees early.