Variations Among Crop Seasons and Inoculum Availability Have a Higher Impact on Grapevine Rust Epidemics Than Training Systems or Plastic Cover

Canopy management practices can be effective as part of the integrated management of grapevine diseases. This study aimed to determine whether training systems and plastic covers can contribute to prevent Asian Grapevine Leaf Rust (AGLR) development. Additionally, the influence of crop season and inoculum availability on AGLR development was investigated. Six-season experiments were carried out to characterize 16 epidemics that developed from natural (NI) or artificial inoculum sources (NI+AI), conducted in different training systems and with or without the plastic cover. The Richards model was fitted to each AGLR disease progress curve to estimate and compare the onset and intensity of epidemics using eight curve elements. Principal components analysis (PCA) identified the incidence progress rate, the area under severity progress curve, final disease severity, time to disease onset, and time to reach the inflection point as the main descriptors for AGLR epidemics. The results showed that AGLR epidemic development was related mainly to differences in inoculum availability and climatic conditions throughout the seasons and to a lower extent to the training system and plastic cover. The earliest disease onset was observed in epidemics when the natural inoculum was supplemented with an artificial inoculum source. Differences in AGRL intensity were correlated to accumulated precipitation, being less severe in autumn-winter than in the spring-summer season. The present findings provided a better understanding of the structure and the seasonal variation of AGLR in 'Niagara Rosada'. The strategies for reducing and/or delaying inoculum build-up among seasons were discussed.