Leaf wetness simulation model and its impact on grapevine downy mildew (Plasmopara viticola) forecasting in Tuscany (Italy)

The availability and the study of meteorological variable trends are of great concern for crop management and protection. Among those, leaf wetness duration (LWD) is strongly related with the development and the outbreak of plant diseases because many important pathogens require a layer of water to move on the surface of plant organs and to start their infective processes. In particular, grapevine downy mildew (Plasmopara viticola) is an important water-related disease that every year could potentially cause heavy losses of production quantity and a reduction of its quality. The main problem is that LWD is not considered a true agrometeorological variable and for this reason a series of problems has to be faced for its detection. The simulation of surface wetness duration is a well-known alternative to measurement. In this work a surface wetness model designed for grapes was applied for the simulation of LWD. The model, called SWEB, uses meteorological variables of air temperature, relative humidity, precipitation and net radiation below and above the grape canopy. Measured LWD and SWEB output were then used to feed Plasmo, a simulation model for downy mildew infections applied in Tuscany (Centre of Italy) and well validated on Sangiovese variety. The results were compared in order to establish if a simulation model for LWD can be used instead of sensors for the simulation of grapevine downy mildew, and then if it can be operationally used for the management of crop protection activities.