Effects of different fungicide treatments on grape, must and wine quality

The aim of this study was to evaluate the effectiveness of natural products and low-rate copper formulations against grapevine downy mildew, in order to reduce or replace copper use in organic farming, and to assess the effects on the qualitative parameters of grape, must and wine of the different treatments. The trial was carried out in an organic vineyard in accordance with the EPPO/OEPP guidelines. Plots were prepared, each containing 12 vine-plants and repeated four times in randomized blocks. At harvest, representative grape samples were picked off from the plots treated with the different products: for each treatment, a random sub-sample was kept for analyses, the remaining part was processed to produce wine. Grapes, musts and wines were characterized for their food quality indices, as well as for their nutraceutical profiles and antioxidant activity. On must and wine, sugars, acidity and pH were determined according to official methods. On grape and wine, total polyphenol, flavonoid and hydroxycinnamic acid contents were determined by spectrophotometric analysis, as well as antioxidant activity tests. Organic acids and single polyphenols were also determined by HPLC. The results of the trial, characterized by moderate infection pressure, indicate that all tested products guaranteed a satisfactory control of Plasmopara viticola although the alternatives to copper were not as effective as copper. Data evidence that grape quality and its oenological potential were not significantly influenced by applied treatments and that they did not significantly differ in comparison with the untreated control, only with an interesting significant negative correlation between proanthocyanidins level and the severity of disease on ripe berries. The uniformity of data seems to evidence a general adaptation of plants to different treatment stresses, probably due both to low input of active ingredients and to moderate downy mildew infection.