Adaptation of the VitiMeteo forecasting system to PIWIs


Abstract: Fungus-resistant grapevine cultivars (PIWIs) are an effective measure to reduce
fungicides in viticulture. Nevertheless, targeted fungicide applications are recommended, to
prevent development of P. viticola genotypes able to overcome PIWI resistance. Optimal timing of fungicide applications in traditional cultivars can be achieved by using decision support systems like VitiMeteo ( While traditional cultivars are highly susceptible to P. viticola throughout the season, fungicide applications in PIWI vineyards should be timed according to the resistance of the individual cultivar. Hence, the objective of the present work was to identify the most susceptible developmental stages of grapevine clusters and leaves. From 2020 to 2023, two traditional and six PIWI cultivars were analyzed in lab and greenhouse experiments. PIWIs showed low sporulation on leaves, while susceptibility in traditional cultivars decreased with increasing leaf age. In clusters, resistance increased cultivar-dependent as phenological development progressed. Traditional cultivars became resistant to P. viticola at the beginning of ripening. PIWIs showed strong resistance during or immediately after flowering dependent on the tested cultivar. Results were integrated into VitiMeteo. Practicability of the extension VitiMeteo PIWI was validated in field trials during the years 2022 and 2023.

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