Climatic risk of grape downy mildew (Plasmopara viticola) for the State of São Paulo, Brazil

Abstract

Viticulture in Brazil has been growing in importance in recent years. In the State of São Paulo, a significant percentage of the production is basically destined to in natura consumption and, more recently, much effort has been made by institutions to revitalize the viticulture in the State. Among fungal diseases, the downy mildew (Plasmopara viticola) is one of the main diseases affecting this crop in Brazil, with extreme damage effects on its production. The objective of this study was to estimate the incidence of the downy mildew on grape under the climatic conditions of the State of São Paulo, based on a mathematical model and using Geographical Information System - GIS tools. The study considered the months from September to April, a period in which the downy mildew can affect grapevines under development. Mean temperature and relative humidity were the basic weather data entered in the GIS database. Leaf wetness duration was estimated from relative humidity measurements. Climatic data entered in the GIS were used to calculate and produce maps depicting the severity of the grape downy mildew, through the application of a disease model. Three cities were evaluated (Jales, Jundiaí, and São Miguel Arcanjo), since they represent the main vineyard centers in the State. The adopted methodology permitted quantifying the severity of the grape downy mildew not only in spatial terms, identifying the variability among the different regions of the State, but also in temporal terms, along the months, making an adequate distinction of the studied cities.