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Overall yield. No significant effects were found on vine vegetative measurements as a result of either shoot or cluster thinning. Despite the lack of differences in vegetative measurements, an increase in fruit quality was observed when either shoot thinning or cluster thinning alone was applied. The response of Blanc Du Bois grown in a subtropical climate differed compared to other hybrid grape varieties examined in previous research when shoot and cluster thinning were applied. Freeze damage in 2013 reduced fruit yield and quality, as well as negatively affected vine performance making treatment effects difficult to separate from vine damage, therefore additional research needs to be conducted to understand the impact of these cultural practices on vine growth and fruit quality in Blanc Du Bois.
Abstract: This study investigated the effect of cluster thinning on the quality and nutraceutical content of 'Chambourcin', 'Pinot noir' and 'Cabernet franc' wine grape berries and wines. In addition, this study investigated SO2 interference on wine nutraceutical content determination. In experiment 1, three vintages of Chambourcin and one vintage of Pinot noir crop level treated wines were evaluated for their composition, anthocyanin, total phenolic, antioxidant and total resveratrol content. Cluster thinning did not affect basic wine composition except pH. Cluster thinning, however, increased the total anthocyanins, total phenolics, and antioxidant capacity. Cluster thinning also increased the total resveratrol level in Chambourcin but not in Pinot noir wines. In experiment 2, we evaluated the effect of cluster thinning on yield parameters, vine growth, fruitfulness, canopy parameters, composition, anthocyanins, total phenolics and antioxidant capacity of 'Chambourcin', 'Pinot noir' and 'Cabernet franc' berries. We found that reponses cluster thinning treatments appear to be confounded with cold injury. Cluster thinning reduced yield in one out of two years of 'Chambourcin' and 'Pinot noir' vines. Cluster thinning increased cluster weight of Chambourcin but not Pinot noir and Cabernet franc. Cluster thinning decreased cropload of Chambourcin and one year of 'Pinot noir' vines. 'Pinot noir' vines under low crop level treatments had the most clusters/vine count prior to cluster thinning in 2004. Cluster thinning increased the anthocyanins, total phenolics and antioxidant capacity of Chambourcin berries linearly independent of harvest date. In experiment 3, we evaluated the extent of sulfite content interference on antioxidant determination (FRAP and ABTS assay) in red and white wines. Addition of SO2 up to 200 mg/L increased antioxidant capacity significantly. Addition of 100 mg/L SO2 generated on average 6.6 % and 64 % increase in antioxidant capacity for red and white wines, respectively indicating the extent of interference was much more pronounced in white compared to red wines.
Vineyard management strategies, including vineyard floor management and crop level management, can be used to influence vine vigor and fruit composition. Two studies were conducted to evaluate the impact of these practices on Pinot Noir in Oregon's Willamette Valley. Managing crop levels is common in cool climate vineyard production though it is a costly practice. With economic pressures, the premium winegrape industry is questioning whether they can reduce production costs and increase yields without compromising quality. A crop thinning trial was conducted in 2010 and 2011 to address these concerns and to better understand the role of vine balance on fruit composition. Crop levels were moderately (35% crop removed) or severely (65% crop removed) thinned at pre-bloom, fruit set, lag phase, or véraison and compared to full crop treatments. In both years, crop thinning reduced yields but had no effect on berry weight or cluster size. In 2010, poor fruit set reduced overall yields, and thinning treatments resulted in very few differences in vine growth, cluster architecture or fruit composition, including total soluble solids (TSS), pH, titratable acidity (TA), yeast assimilable nitrogen (YAN), anthocyanins, phenolics and tannins. In 2011, yields were much higher due to high fruit set and larger cluster size. No differences were found in vine growth (leaf areas or pruning weights) or fruit YAN, but thinned vines had higher TSS and pH and lower TA than full crop vines at harvest. Fruit thinned at lag phase and véraison had higher TSS and lower TA than fruit thinned pre-bloom. Intensity of thinning had a stronger influence on anthocyanin and tannin concentration than timing, while phenolics were not impacted by either factor. Ravaz index values (fruit yield/pruning weight) below 2.25 and leaf area to yield ratios of 2.25 to 3.25 m2/kg improved fruit composition in 2011 as did later season thinning, though data from the remaining years of this study will provide more insight into appropriate crop load metrics for cool climate Pinot Noir. A second study was implemented in 2011 to determine the impact of crop thinning in vines with different levels of vegetative vigor caused by three vineyard floor management techniques: permanent grass (Festuca rubra spp. rubra) cover (grass), alternating grass cover and tillage (grass & tilled), and tillage of every alleyway (tilled). Crop was thinned at the BB stage of berry development (EL stage 73) to one cluster per shoot (half crop) or not thinned (full crop); all cluster wings were removed at the time of thinning. Tillage treatments had been in place four years prior to the start of the study and competition for nitrogen in grass caused reduced early season vine growth, leaf chlorophyll and canopy size at both bloom and véraison while crop thinning increased canopy size at véraison. Yields were altered by tillage and crop thinning treatments, as grass had fewer clusters per shoot and berries per cluster, and crop thinning reduced yields to 64.7% of full crop across all tillage treatments. At harvest, grass had the lowest TA while TSS and pH were not affected by tillage. Crop thinning increased TSS but did not impact pH or TA. Anthocyanins were affected by both tillage and thinning and were found to be related to vine yield, YAN, leaf N, and leaf area index. Tannins were highest in grass but were not affected by crop thinning, and phenolics were not changed by either factor. Few interactions between tillage and crop thinning were found, but as variables such as yield per vine were impacted by both treatment factors, monitoring long term effects of crop.
‘MidSouth’, a relatively low maintenance interspecific hybrid bunch grape currently grown in South Mississippi, has low sugar and high acid levels for red wine use. Two studies, conducted at the Mississippi State University McNeill Research Unit in 2020 and 2021, determined the effects of pruning timing, leaf removal, and shoot thinning on ‘MidSouth’ development and fruit and wine quality. Treatments in the first study included early versus normal pruning timing, both with and without leaf removal, and treatments in the second study included leaf removal, shoot thinning, and control vines. Cluster temperatures, leaf chlorophyll, berries per cluster, berry and cluster weights, crop yield, Ravaz index, total soluble solids, titratable acidity, juice pH, monomeric anthocyanin pigment, and total phenolic content data were collected. It was determined that ‘MidSouth’ fruit quality can be altered through canopy manipulation, but not enough of a desired effect was achieved for these practices to be recommended.