Incidence of vine sprayings with downy mildew fungicides, without parasitic fungi, on Cabernet Sauvignon grapes and wines composition

Abstract

Vine sprayings with fungicides is necessary in most vineyards of the world since the second half of the 19th century in order to control parasitic fungi particulary downy mildew (Plasmopara viticola) and powdery mildew (Uncinula necator). During more than 50 years, copper and sulphur fungicides have been the only agents active against these deseases. Since the 50th, losts of organic products have been developed to control parasitic fungi. Meanwhile, the viti-vinicultural sector has progressively taken in consideration indirect consequences of vine sprayings on toxicological, environmental and oenological aspects. About oenological aspects, numerous publications concern the consequences of vine sprayings on fungicide residues in must and wines as on development of fermentations, volatile sulphur defaults in wines as on grape maturation and wine quality. However, studies concerning the consequences of fungicide sprayings, against downy mildew, on grapes and wines composition have been realized using reference vines sprayed with organic fungicides. Most part of Chilean vineyard is not concerned by the downy mildew. So, it is possible in this vineyard to keep a reference vine without any spraying against this fungus and to compare grapes and wines composition obtained from vines sprayed with fungicides or not. Close to Santiago de Chile, cabernet sauvignon vines were sprayed during all vegetative period with different fungicides (only folpet, folpet then copper, folpet and fosetyl-Al mixture) following a random-block scheme (Fischer blocks) with three repetitions for each fungicide spray. Grapes and wines composition were compared with those from a reference plot without any spraying against mildew. Fungicide sprayings didn’t significantly modify sugar composition, nor titratable acidity and pH during cabernet sauvignon grapes maturation unless it should be noted that the percentage of veraison was significantly higher in the initiation of grapes maturation. Some significant variations in 3-mercaptohexanol content, a varietal thiol of cabernet sauvignon wines, after alcoholic and malolactic fermentation were noted with copper sprayings. This result from copper reactivity with thiols. Variations in anthocyanin concentrations in grapes and wines were also observed but vine sprayings didn’t give anthocyanin concentrations at harvesting in grapes or in wines after vinifications at lower level than in reference grapes and wines. Globally, in this experimentation, fungicide sprayings didn’t lead to a significant modification of wines composition.