- Fruits: grapes
- Production Systems: general crop production
Cabernet Sauvignon and Cabernet Franc are two important wine grape varieties grown in the Eastern United States for which improved knowledge of the relation between crop yield and quality is critically important to sustainability. Crop yield is generally inversely correlated with measures of wine grape and wine quality. Furthermore, the yield of the vine must be in balance with the vigor of the vine. Specifically, the ratio of canopy leaf area to crop weight must be optimized for quality wine grape production. In this study we seek to determine whether increasing the canopy area to crop weight ratio by decreasing the yield per vine will significantly improve the quality of wine grapes and wine produced. We will do so by examining the effect of two different levels of cluster thinning on grape and wine quality. Modifying the crop yield in this manner will allow comparisons of the quality of wine grapes and wine for a range of crop yields over a 2 year period. Besides using grape soluble solid content (°Brix) as a quality measure, expanded wine measures including total phenol content and wine tasting scores also will be used. A better understanding of the relationship between quality and yield, particularly for low yield levels, will help in improving both wine quality and consistency from winery to winery and from year to year. Furthermore, since the current pricing of wine grapes is largely based on yield for a given variety of grapes then information regarding optimal yields is crucial to sustainable winegrowing in the Eastern U.S.
Project objectives from proposal:
Specifically, we will test the hypothesis that there is no difference in wine grape or wine quality with one cluster per shoot versus two clusters per shoot for each of these varieties. This simplifies this potentially complex issue so that it becomes an examination of the effects of two levels of cluster thinning. Both levels of cluster thinning are considered currently acceptable practices for these varieties. Wine grape quality will be measured by total phenol content,anthocyanins,°Brix, pH and total acidity. Wines will also be evaluated for overall quality by an independent wine tasting group. Wine grape and wine quality parameters will be compared for the two clusters and one cluster per shoot treatments. Each quality parameter will be analyzed for significant differences between the two treatments using Student's t-test or another appropriate method if needed. As there can be variability in fruit set and fruit weight by season this trial will be carried out over two successive growing seasons. This should provide us with a wider range of crop yield at each cluster thinning level as well as a different set of weather conditions. These additional data points may aid in evaluating the optimum canopy area to crop yield by providing greater statistical power. Through annual measures of pruning weights we will also track whether vine vigor is significantly different for the two levels of cluster thinning.