Healthy grapes make better wine




It`s no surprise that severely diseased grapes make poor wine. However, we found that even trace levels of powdery mildew set in motion a sequence of events that results in severely downgraded and wine that could not be sold. The damage is not due to the powdery mildew itself, but to how it shifts the naturally occurring (and normally beneficial) microbial community on grape berries towards one that produces foul flavors and odors during winemaking.


Consistent production of a high-quality product is paramount to expansion of the New York wine industry beyond state borders. Powdery mildew is the most destructive disease of grapes, and was known to affect wine quality when severe. In the course of another study, we noticed that trace levels of powdery mildew increased the severity of rots by other fungi. Could trace levels of powdery mildew also affect wine quality?


For five years, an interdisciplinary group of plant pathologists, entomologists, enologists, and food chemists studied how trace levels of powdery mildew (diffuse powdery mildew) resulted in poor quality wines. The key to the puzzle was infection of the berries during a brief period immediately before they acquired natural resistance three weeks after bloom. This resulted in a healthy-appearing, but microscopically wounded skin. The berries were then colonized by spoilage microbes. In turn, they released volatiles that attracted insects that furher wounded the berries and caused more decay. In the end, the spoilage microbes took part in the fermentation process, and ruined the wine.


Once the problem was understood, it was easily corrected. A minor adjustment in the timing of fungicide sprays largely eliminated diffuse powdery mildew, and all of the attendant problems. An insidious cause of wine spoilage was thereby eliminated with no increase in either cost or pesticide use.

Submitted by: 

  • Gadoury, David M

Researchers involved: 

  • Seem, Robert C
  • Ficke, Andrea
  • Wilcox, Wayne F
  • Loeg, Gregory
  • Henick-Kling, Thomas
  • Conterno, Lorenza

International focus: 

  • United States of America
  • Argentina
  • Australia
  • Chile
  • France
  • Germany
  • Hungary
  • Italy
  • Portugal
  • South Africa
  • Spain
  • Switzerland

United States focus: 

  • Delaware
  • New York

New York State focus: 

  • Cayuga
  • Chautauqua
  • Columbia
  • Delaware
  • Dutchess
  • Nassau
  • Niagara
  • Ontario
  • Orleans
  • Schuyler
  • Seneca
  • Suffolk
  • Tompkins
  • Wayne
  • Yates