Cercospora leaf spot of olive: inoculum production and infections timing throughout the year

Cercospora leaf spot (CLS), caused by Pseudocercospora cladosporioides, is one of the most significant foliar diseases impacting olive production. Over two consecutive years, we investigated the temporal variation of inoculum production and the timing of foliar infections throughout the year on the Arbequina cultivar located in the northwest of Uruguay. Additionally, we examined the influence of meteorological variables in both inoculum production and the occurrence of infections. Two periods characterized by substantially higher spore production were identified, one during late spring to early summer and the other during autumn, both favored by temperatures of 20-25 °C and relative humidity between 80 and 95%. The lowest production was registered in winter explained by frequent days with temperatures below 10 °C. Infections occurred throughout the year, with a significant decrease during the early spring, probably due to a low spore available in the field and the less susceptibility of young leaves to be infected. These findings will help growers design effective management strategies focusing on the highest inoculum production periods, especially in autumn when the infections are more abundant.