Cropload Management of ‘Vidal blanc’ Improves Primary Bud Cold Hardiness and Maintains Berry Composition in the Lower Midwestern United States

Abstract

Canopy architecture, yield components, berry composition, pruning weight, Ravaz Index, and midwinter primary bud cold hardiness of own-rooted ‘Vidal blanc’ (Vitis vinifera × Vitis rupestris) were measured in response to balanced pruning formula treatments of 20, 30, or 40 nodes retained for the first 454 g of dormant pruning weight and an additional 10 nodes for each additional 454 g and three cluster thinning levels of one, two, and two+ clusters per shoot in 2006 and 2007. Although the pruning formula affected the distance between shoots along the canopy, and the number of count shoots per hectare, the canopy leaf layer numbers were unaffected in either year. Application of the pruning formula did not affect components of yield in either year. However, the number of clusters and yield per vine were affected by cluster thinning treatments where they increased linearly with the decrease in its severity, explaining 73% and 77% of total variance in yield in 2006 and 2007, respectively. Pruning formula or cluster thinning did not affect berry composition substantially. Cluster thinning improved the percentage of mature nodes on shoots before a killing frost in both years. Cluster thinning to one or two clusters per shoot also improved the lethal temperature killing 50% of the primary buds compared with no cluster thinning in both years of the study. Mature wood weight and total pruning weight displayed a quadratic response to cluster thinning where two clusters per shoot had the greatest weight for both, whereas pruning formula had no effect on pruning weight. Optimum fruit weight–pruning weight ratio was achieved with the 30 + 10 pruning formula and two clusters per shoot cluster thinning treatments in both years of the study. The results of this study provide valuable information for growers of interspecific hybrids such as ‘Vidal blanc’ in the lower midwestern United States as well as in other regions with long, warm growing seasons. Balanced pruning to 30 nodes per 454 g of dormant prunings and cluster thinning to two clusters per shoots optimized yield, maintained fruit composition, improved primary bud cold hardiness, and achieved an optimum fruit weight-to-pruning weight ratio of 10.0 kg·kg–1. Thus, this approach should be used for ’Vidal blanc’ in the lower midwestern United States to sustain production.