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Thomas M. Todaro and Imed E. Dami

‘Cabernet franc’ grapevines (Vitis vinifera) sustained severe winter injuries of all aboveground parts following two consecutive freezing events in 2014 and 2015 in Ohio. To ensure grapevine recovery, adjustment of pruning and training practices must be accomplished. However, optimum training of new shoots for trunk replacement was not known and research-based information on this topic was lacking. Therefore, the purpose of this study was to evaluate different training and pruning methods for trunk renewal and recovery of ‘Cabernet franc’ and their impacts on growth, yield, cropload, and fruit composition following severe winter injuries. In 2016, grapevines were manipulated using a combination of training [Fan, vertical shoot positioning (VSP), or both], pruning (cane- or spur-pruned), and trunks (two, four, or more trunks per vine). The Fan system took less time to train than VSP during the growing season; however, the latter took less time to train and prune during the following dormant season. Training and pruning methods with increased buds per vine resulted in increased shoots, leaf area, pruning weight, clusters, and yield per vine but decreased juice total soluble solids (TSS). The exceptions were vines with combined training systems of Fan and VSP, in which leaf areas and pruning weights were reduced despite increased bud count per vine after pruning. In conclusion, each system has advantages and disadvantages; however, the Fan training system with cane pruning and multiple trunks produced the most optimum trunk size, yield, cropload, and fruit composition. Therefore, following trunk freeze injury, we recommend retaining all shoots using the Fan training during the growing season. During the subsequent dormant season, growers should select medium-sized canes for trunk replacement and train four trunks and four canes for the VSP system.

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S. Kaan Kurtural, Imed E. Dami, and Bradley H. Taylor

Response of yield components and fruit composition of `Chambourcin' (Vitis vinifera × V. rupestris) grapevines to three pruning levels of 15, 20, and 25 nodes retained for each pound of dormant prunings; and three cluster thinning levels of 1, 2, and 2+ clusters per shoot in 2002 and 1, 1.2, and 1.5 clusters per shoot in 2003 were measured at two vineyards in the lower midwestern United States. In both years of the study, there was very little interaction of pruning and cluster thinning. The proportion of non-count shoots increased within the canopy in response to increased pruning severity. Pruning weight means were lower in 2002 across all treatments compared to 2003. Pruning weights decreased with the increase in the number of clusters retained per vine. Pruning influenced yield only in 2003 when the proportion of count shoots decreased below 62% of the total, hence the relationship between number of shoots per vine and yield (R2 = 0.3452; P < 0.0003). In both years of the study, the increase in severity of cluster thinning resulted in yield reduction but an increase in the total soluble solids in juice. Yield compensation was achieved by an increase in cluster weight of 38%, and 25% in response to a reduction of 37%, and 23% in cluster numbers; which translated into a yield reduction of only 10% and 3%, at Vineyards 1 and 2, respectively. Balanced pruning to 15 to 20 nodes per 1 lb of prunings and cluster thinning to 1 to 1.2 clusters/shoot optimized yield (9.7 kg/vine, 13.4 t·ha-1) and fruit composition, and maintained vine size (≥0.3 kg·m-1 of row). These results provide valuable information for growers of `Chambourcin' grapevines in the lower midwestern U.S., as well as in other climates with long growing seasons.

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Imed E. Dami, Shouxin Li, Patricia A. Bowen, Carl P. Bogdanoff, Krista C. Shellie, and Jim Willwerth

Economic loss due to cold weather events is a major constraint to winegrape (Vitis vinifera) production and wine-related industries where extreme and/or fluctuating winter temperatures induce injury and require remedial retraining and replanting increases production costs and lowers yield and fruit quality. The purpose of this study was to determine whether a foliar application of abscisic acid (ABA) could increase the freezing tolerance (FT) of field-grown, ‘Chardonnay’ winegrape and whether its effectiveness can be influenced by the phenological timing of the application. Mature ‘Chardonnay’ grapevines were treated with a foliar application of ABA at a concentration of 500 mg·L−1 at vine phenological stages corresponding to 50% véraison, postvéraison, and postharvest. Results from field trial sites located in four distinct winegrape production regions in the United States (Idaho and Ohio) and Canada (British Columbia and Ontario) showed that foliar application of ABA increased bud FT, primarily during autumn cold acclimation. Foliar ABA application had no consistent influence on bud FT in midwinter or during spring deacclimation, or on percent budburst in spring. Vine phenological stage at the time of ABA foliar application influenced ABA effectiveness, although results were inconsistent among locations. At most locations, applications made at véraison or postvéraison were more effective than applications made postharvest. No phytotoxic response or adverse changes in yield or berry composition were detected in response to ABA application. The consistent increase in bud FT during autumn cold acclimation observed at all trial locations in this study indicates that foliar ABA, applied at véraison or postvéraison, can reduce the risk of economic loss due to cold injury in production regions with frequent early autumn cold weather events.