Spatial and Seasonal Characterization of Climatic Favourability for Neonectria ditissima and Initial European Canker Development in High‐Altitude Apple‐Producing Regions of Southern Brazil

ABSTRACT

Apple production in southern Brazil is responsible for all national output. However, production is limited by phytosanitary constraints, particularly European canker (EC), caused by Neonectria ditissima . In this context, understanding the climatic factors associated with the infection and development of EC is essential to support more effective and sustainable management strategies. This study aimed to characterize the spatial and seasonal climatic favourability for N. ditissima infection and the initial development of European canker in some of the most productive high‐altitude apple‐producing regions of southern Brazil using the R _m risk model proposed by Kim and Beresford. The R _m risk model integrates rainfall frequency, precipitation amount, and the average number of daily hours with temperatures between 11°C and 16°C into a dimensionless indicator of climatic favourability, based on historical meteorological data from 2016 to 2024 for some of the most productive high‐altitude apple‐producing regions in southern Brazil. The R _m risk data were aggregated on a monthly scale to assess seasonality, seasonal distribution and interannual variability of climatic risk. Intermediate to high R _m values were observed in some of the most productive high‐altitude apple‐producing regions, including Painel, São Joaquim and Urupema, indicating highly favourable climatic conditions for N. ditissima infection and the initial development of EC. Intermediate to high R _m risk values were predominantly concentrated from autumn through spring, with the highest seasonal mean values generally occurring during spring and autumn. In contrast, the lowest risk levels were observed during summer (December to February), with low interannual variability. This pattern indicates the presence of recurrent seasonal risk periods associated with increased environmental favourability for N. ditissima establishment, spread and early EC development. The results demonstrate that some of the most productive high‐altitude apple‐producing regions exhibit persistent climatic suitability for N. ditissima infection and initial development of EC, reinforcing the relevance of the R _m risk index. Although it should not be interpreted as a direct predictor of disease incidence, it provides a quantitative epidemiological framework for identifying climatic risk patterns and supporting future validation, forecasting and integrated disease management programs in high‐altitude apple‐producing regions of southern Brazil.