ISHS Acta Horticulturae 427: Strategies to Optimize Wine Grape Quality
SULFUR RESIDUES ON WINE GRAPES |
| Authors: | G.A. Sawyer Ostrom, B.H. Gump, V.E. Petrucci |
| Keywords: | powdery mildew (Uncinula necator), fungicides, hydrogen sulfide, sensory analysis |
| Abstract:
From 1990 to 1992, French Colombard and Zinfandel grapes were sprayed with sulfur products and/or ergosterol biosynthesis inhibitor (EBI) fungicides to evaluate control of powdery mildew (Uncinula necator). The wines made from the treatments were evaluated for the presence of sulfur-related sensory attributes. Materials included dust, wettable, and micronized sulfur products and EBI fungicides (Bayleton in 1990, Rally in 1991 and 1992). Treatments ranged from an untreated control, to sulfur dust only all season, plus several combination sulfur/EBI fungicide treatments. Powdery mildew levels were checked in mid-July each year. Sensory triangle difference tests were performed on the wines made from each treatment in 1991 and 1992. No mildew was present in 1990 or 1991. The proportion of infected clusters was not significantly different between treatments and the untreated control in 1992; infection ranged from 7.5% to 15.6% infected clusters in the French Colombard, and from 6.0% to 18.0% infected clusters in the Zinfandel. Zinfandel wines made from treated grapes had detectable differences from the untreated control in both 1991 and 1992 for most treatments (p<0.01) when Montrachet yeast was used. In 1992, treated Zinfandel wines made with Enoferm Burgundy yeast were not as readily distinguishable from the untreated control, with the exception of the EBI fungicide only treatment. French Colombard wines made from treated grapes also had detectable differences from the untreated control in both 1991 and 1992 for most treatments (p<0.01) when Montrachet yeast was used. In 1992, treated French Colombard wines made with Fermichamp yeast were all highly distinguishable from the untreated control (p<0.001) except for the micronized sulfur first two applications/late sulfur dust treatment. All treatments were equally effective in controlling mildew, but it appears that there is a concern when sulfur is used on grapes that are then made into wine. Differences between treatments and the untreated control were very apparent, particularly in the Zinfandel treatments, and particularly with Montrachet yeast. | |
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