Validation of a warning system to control brown rot in peach and nectarine

Monilinia spp. is the main pathogen that affects stone fruit, causing significant production losses, especially in seasons with favorable climatic conditions for disease development. Currently, the standard practices for controlling this disease are by means of spray programs of synthetic fungicides. Fungicide applications using treatment schedules imply an increase in the number of applications; however, the applications are justified considering the real risk of Monilinia spp. infection. Consequently, fruit surface contains a higher number and concentration of residues, but not better control of the disease. From previous studies, the epidemiology of Monilinia spp. was deeply studied in one of the main stone fruit regions of Europe, the 'Valle del Ebro', and an epidemiological model was developed to describe the brown rot epidemic pattern in this area. After that, a warning system for fungicide applications in the field was elaborated that included the main factors to be considered as fruit susceptibility, the presence of inoculum in the field, and climatological factors (temperature, leaf wetness, rainfall, or their interaction). In the present study, we present data of the warning system validation during six seasons in 38 fields of peaches and nectarines of the 'Valle del Ebro'. The results indicated that the incidence of disease caused by Monilinia spp., recorded in the field and postharvest, was similar in both plot evaluations and the calendar and warning systems. However, the disease level was higher in late varieties (3.2% and 9.3% of infected fruit recorded in the field and in postharvest, respectively) in comparison with earlier varieties (0.6% and 3.1% of infected fruit recorded in the field and in postharvest, respectively). In general, the strategy applied (the calendar or warning system) did not affect the disease level recorded. However, when fungicide treatments were applied following the warning system, the treatment reductions were higher than 50% in 96% of the trials in early varieties; meanwhile, in late varieties, this level of reduction was obtained in 77% of trials. Our data encourage the use of the proposed warning system as an effective strategy to control Monilinia spp. in peaches and nectarines, reducing the number of chemical treatments applied in the field with a high level of efficacy

This research was funded by a Catalan project (PDR 2014-2020) and the CERCA Program (Generalitat de Catalunya).