VitiMeteo Plasmopara – Practical application of the PIWI Add-on

Abstract: Downy mildew, caused by Plasmopara viticola, is one of the most destructive
diseases in viticulture worldwide and is traditionally controlled through intensive fungicide
applications. Disease-resistant grapevine cultivars (PIWIs) offer considerable potential to
reduce fungicide input; however, their varying levels of resistance require cultivar-specific plant protection strategies. The VitiMeteo forecasting system has been expanded to account for PIWI cultivar susceptibility in downy mildew risk prediction. VitiMeteo PIWI enables winegrowers to tailor fungicide applications to the resistance level of individual PIWI cultivars. This cultivarspecific approach contributes to a significant reduction in fungicide use in years with low to moderate disease pressure, while ensuring effective crop protection through an adequate number of applications in years with high infection risk.
In 2024, southern Germany experienced a particularly severe P. viticola epidemic. In a
field trial with the cultivar Johanniter (Rpv3.1) at the Freiburg State Winery, disease severity
on bunches in the untreated control reached 82 %, with a disease incidence of 98 % on 18 June. In contrast, assessed on 21 August, the treated plot showed a disease severity of 8 % and an incidence of 81 % on bunches after ten treatments, confirming the output of the VitiMeteo PIWI application.