Epidemiology of Monilinia laxa, the causal agent of blossom blight in almond orchards within the Ebro Valley

Almond blossom blight, caused by Monilinia spp., is a notable fungal disease associated with intensified crop management practices. In this study, we aimed to investigate the epidemiology of Monilinia spp. on almonds in two orchards in the Ebro Valley, with a focus on (i) primary inoculum sources through sampling of affected mummified fruiting structures from trees and the ground before blooming; (ii) secondary inoculum sources postblooming; and (iii) disease dynamics throughout the season in relation to meteorological data. Monilinia laxa was the primary species affecting almonds in the Ebro Valley. Furthermore, early-stage mummified fruiting structures frequently adhered to branches (3.8 log conidia/mummified fruiting structure), whereas late-stage mummified fruiting structures were predominantly found on the ground. Additionally, cankers present before blooming (6.0 × 102 and 1.4 × 103 conidia/canker) served as primary inoculum sources. Inoculum incidence and concentration were significantly higher in late-stage fruits (50-100%, 8.5 × 103-2.5 × 105 conidia/plant organ) than those in flowers (20-30%, 2.0-4.0 × 103 conidia/plant organ) or those in postblooming cankers (1.0 × 102-1.8 × 103 conidia/canker). Infection dynamics of blossom blight in both orchards peaked during the last third of April under favorable meteorological conditions, specifically within the 10 days preceding the assessments. Significant correlations were found between infections progression and meteorological parameters, including temperature, relative humidity, rainfall and leaf wetness. These findings provide critical insights into sustainable disease management practices and the optimal timing of protective measures against blossom blight.