Downy mildew of grapevine is one of the most devastating diseases in viticulture. The disease-causing pathogen Plasmopara viticola finds especially good conditions in humid years with frequent rainfalls and can then lead to severe damage in the vineyard. This is particularly problematic because all traditional Vitis vinifera varieties cultivated in European countries have a high susceptibility to this pathogen. Therefore, winegrowers treat these grape varieties with fungicides at an average of 12-15 times per year to keep leaves and grapes healthy until harvest (Pertot et al., 2016). Whereas conventional estates have access to a wide range of synthetic fungicides, organic winegrowers rely mainly on copper fungicides (Gessler et al., 2011). However, the amounts for copper application are restricted to a maximum of 28 kg within seven years (4 kg/ha/year) in the European Union (Commission Implementing Regulation (EU) 2018/1981). German eco-associations have furthermore committed themselves to 17.5 kg within five years (3 kg/ha/year with option to increase up to 4 kg/ha/year at high infection pressure). Years with particularly high P. viticola infection pressure like 2016 and 2021 in Germany therefore lead to existential problems in the organic wine-growing industry, especially since potassium phosphonate is banned in organic winegrowing since 2013 (Bleyer et al., 2020). Moreover, negative effects of copper on the environment like a reduction in biodiversity of soil micro- and macroorganisms (Merrington et al., 2002; Buenemann et al., 2006) were reported. Authorities and environmental organizations have therefore been calling for a reduction in copper fungicides for many years. Since 2019, major research institutes in the winegrowing sector in Germany have joined in the VITIFIT project (www.vitifit.de). The aim of this project is to develop new strategies, particularly suitable for organic viticulture, to reduce the amount of copper fungicides in P. viticola control.
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