Uncertain weather patterns raise concerns about frequent spring frosts and injury in grapevines. This article quantifies growers' perceptions of susceptibility to spring frosts and examines their satisfaction with existing mitigation strategies. Results from a survey with grape growers show that over 80% of sampled growers have experienced damage due to frosts. Over-vine sprinklers, proper site selection, and adoption of late budding cultivars are the practices with the highest satisfaction levels. None of the strategies examined reached the highest satisfaction score. In addition, 61% of respondents showed interest in sprayable products to delay budbreak and circumvent grapevine damage.

Temperate regions experiencing sub-zero temperatures negatively impact grapevine yield. Potassium has been claimed as a cryoprotectant to improve cold hardiness in grapevine. This study investigated the effect of foliar application of liquid potassium-based fertilizer, ReaXTM, on cold-hardiness of grapevine Vitis spp. "Chambourcin" along with its effect on yield and fruit quality. The vines were sprayed four to five times between the fruit set and veraison stage at a concentration of 1.5% (v/v) for two consecutive seasons. Petioles were analyzed for nutrients, clusters for yield and fruit quality, and cold hardiness was determined by differential thermal analysis and bud injury assessment. Potassium deficiency was observed in all treatments, and its content did not increase significantly in treated vines. Berry potassium levels and total soluble solids were generally higher in K-treated vines, however, there was no significant effect on yield and other fruit quality traits. Significant differences in cold hardiness levels were observed in both dormant seasons. Foliar application of potassium is a promising cultural practice to increase cold hardiness, but further studies are needed to understand the limits of its effectiveness.

The purpose of this study was to explore the mechanism of ABA-induced freezing tolerance increase in grapevines. The specific objectives were to evaluate the impact of ABA treatment on soluble sugar concentration in grape buds and determine the correlations between freezing tolerance and ABA-affected soluble sugar concentration. Vitis spp 'Chambourcin' and Vitis vinifera 'Cabernet franc' were treated with 400 and 600 mg/L ABA in the greenhouse and field. The freezing tolerance and soluble sugar concentration of grape buds were measured monthly during the dormant season in the field and at 2wk, 4wk, and 6wk after ABA application in the greenhouse. It was observed that fructose, glucose, and sucrose are the main soluble sugars that correlate with freezing tolerance of grape buds and the synthesis of these sugars can be enhanced by ABA treatment. This study also found that ABA application can promote raffinose accumulation, however, this sugar may play a more important role in the early acclimation stage. The preliminary results suggest that raffinose accumulated first in buds, then its decrease in mid-winter corresponded with the increase of smaller sugars, such as sucrose, fructose, and glucose, which in turn, corresponded with reaching maximum freezing tolerance. It is concluded that ABA is a cultural practice tool that can be used to enhance freezing tolerance of grapevines.

Abscisic acid (ABA) plays crucial regulatory roles in cold acclimation and deacclimation of grapevine, making it a potential tool to be utilized in vineyards for the acquisition of preferred phenotypes in winter and spring. To understand the function of ABA, we conducted experiments during cold acclimation and deacclimation and evaluated the impact of exogenous ABA on the grapevine transcriptome. RNA-seq data were collected periodically hours or days after ABA treatment. Transcriptomic data were analyzed using principal component analysis (PCA), hierarchical clustering, unsupervised weighed gene co-expression network analysis (WGCNA), contrast-based differentially expressed genes (DEGs) identification and pre-ranked gene set enrichment analysis (GSEA). Our results suggest that ABA functions differently during cold acclimation and deacclimation by selectively regulating key pathways including auxin/indole acetic acid (IAA) metabolism, galactose metabolism and ribosome biogenesis. We also identified the activation of several apparent negative feedback systems that regulated ABA-induced transcriptomic changes, suggesting the existence of a balancing system in response to excessive ABA. This balancing systems potentially eliminates the long-term negative effect on grapevine growing from using ABA in the field. These findings advance our understanding about the regulation of grapevine physiology during dormancy and supports the potential of applying ABA as a cultural practice to mitigate cold injury in winter and spring.

The production of grapes in the Midwest U.S.A. is not free of challenges. Growers are presented with a long list of strategic and operational decisions when planning a vineyard. This article uses survey data and secondary data to prepare sample budgets and examine costs, expected returns, and economic feasibility of grape vineyards under different production systems. Departing from two sample budgets that resemble the reality of American-hybrid and vinifera grape growers in the Midwest, we examine the economic feasibility of 24 plausible production scenarios by simulating changes in operational and technical parameters of production. Our results show that economies of scale, level of automation, and adequate balance between capital and labor use are determining factors for economic feasibility. Small-scale hybrid vineyards (10 acres or less) are seldom feasible as a stand-alone project. Vinifera vineyards tend to reach superior performance due to scale, decisions regarding automation, and efficiency of field operations. Following the feasibility analyses and results, our discussion helps explain why grape vineyards are frequently integrated with wineries and other business units across the Midwest.

Several winegrape cultivars grown in cool climates, including Vitis sp. 'Chambourcin', are highly productive and require crop regulation to ensure timely fruit maturation and improved fruit quality. Balanced pruning and cluster thinning are the cultural practices used to attain the desired crop load in 'Chambourcin'. However, crop reduction by cluster thinning is labor intensive, costly and typically not mechanized for winegrapes. In this study, the practice of early season leaf removal was investigated as an alternate tool to reduce crop level, thereby optimizing crop load and fruit quality in 'Chambourcin'. The specific objectives were to determine the effects of the timing of leaf removal (pre-bloom, bloom, fruitset, no removal) on yield components, crop load, fruit composition, and cold hardiness. Leaf removal at pre-bloom and bloom reduced yield and crop load (Ravaz index) as compared to control (no defoliation). However, leaf removal did not impact fruit composition. Furthermore, defoliation at pre-bloom and bloom reduced bud cold injury during the dormant season. Therefore, early season leaf removal is a viable alternative to cluster thinning as a vineyard practice for yield regulation in 'Chambourcin' grapevines.

Most viticultural regions in the world annually sustain spring frost injury-associated yield loss. Researchers have developed sprayable products to prevent spring frost injury by delaying budbreak. The goal of this research was to evaluate the efficacy of novel products, including Amigo oil,® ProTone,® and FrostShield,® to delay budbreak and the effect of these products on vegetative and reproductive growth in grapevines. The early budbreaking cultivars La Crescent and Marquette were used in field experiments in 2018 and 2019 and in a growth chamber experiment in 2019. Treatments included a control (no spray), 10% (v/v) Amigo oil, 500 mg/L S-ABA ProTone, and FrostShield. In field experiments, FrostShield consistently delayed the budbreak of both cultivars for four to six days, while the other two products showed a very limited effect. In addition, FrostShield did not affect cultivars’ vegetative or reproductive growth. In the growth chamber experiment, FrostShield delayed the budbreak of two cultivars for more than two weeks, while the effect of the other two products was inconsistent between cultivars. Our results indicate that FrostShield outperformed Amigo oil and ProTone by consistently delaying budbreak without negatively affecting vegetative or reproductive growth, suggesting that FrostShield might be an effective product to prevent spring frost injury.

Previous studies have demonstrated that the freezing tolerance (FT) of grapevine was enhanced by foliar application of exogenous abscisic acid (exo-ABA), a treatment which might be incorporated into cultural practices to mitigate cold damage in vineyards. To investigate the underlying mechanisms of this response, a two-year (2017 and 2018) study was conducted to characterize the effects of exo-ABA on greenhouse-grown 'Cabernet franc' grapevine. In control grapevines, both physiological (deeper dormancy) and biochemical (sugar accumulation in buds) changes occurred, indicating that grapevines initiated cold acclimation in the greenhouse. Compared to control, exo-ABA decreased stomatal conductance 2 h after application. Two weeks post application, exo-ABA treated grapevines showed accelerated transition of grapevine physiology during cold acclimation (increased depth of dormancy, decreased bud water content and enhanced bud FT), relative to control. Exo-ABA induced the accumulation of several sugars in buds including the raffinose family oligosaccharides (RFOs), and the RFO precursor, galactinol. The expression of raffinose and galactinol synthase genes was higher in exo-ABA treated grapevine buds, compared to control. The new findings from this study have advanced our understanding of the role of ABA in grapevine FT, which will be useful to develop future strategies to protect grapevines from cold damage.

‘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.

In 2014 and 2015, Ohio vineyards were exposed to multiple freeze events of -20 degrees C or lower, resulting in vine dieback, i.e., complete damage of above ground parts in Vitis vinifera. Grapevines that sustained dieback were rehabilitated for trunk replacement by training 1-year-old shoots with two distinct morphologies, based on internode diameter of large (L) and normal (N). This study evaluated the impact of cane morphology (L and N) in V. vinifera Cabernet franc on freezing tolerance (FT) of bud, phloem, and xylem tissues in relation to their respective anatomical structures and carbohydrate concentrations. Compared to N canes (7-9-mm diameter), L canes (10-15 mm) in Cabernet franc were considered vigorous and had the following morphological characteristics: long and heavy, with long and wide internode, and presence of numerous laterals. Furthermore, cane anatomy was also different with L canes having a significantly higher number of vascular transport units, xylem vessels, and phloem fibers than those in N canes. Freezing tolerance of buds and phloem was also different between the two cane types, with L canes being more cold sensitive than N canes, especially during fall acclimation and late-winter deacclimation. Sugar concentrations, however, were not different between L and N canes. These results suggest that cane morphology and anatomy play a significant role in affecting FT and the large and abundant anatomical structures of phloem and xylem contributed to the reduced FT of these tissues. In all practicality, this study suggests the best cultural practice for trunk replacement, and vine recovery should include the removal of the undesirable vigorous and cold sensitive canes during pruning.

Soil-hilling around grapevines is required in the eastern United States for winter protection of grafted and cold sensitive grape cultivars (Vitis vinifera). The effects of simazine-treated mulches (STM) on soil temperature, scion rooting, and soil water conservation were measured. Neither simazine nor interactions between simazine and mulches affected any variables measured in this study. Wood and straw mulches increased the minimum temperature of media around the graft union as effectively as hilled soil, reduced scion rooting by a factor of 2 to 75 compared with soil-hilling, and increased soil moisture content 45 to 75% at Wooster and 8 to 23% at Kingsville. These results indicate that mulches have positive attributes and should be considered as an alternative to traditional soil-hilling in vineyards for temperature mitigation around graft union.

Soluble sugars play an important role in freezing tolerance in both herbaceous and woody plants, functioning in both the reduction of freezing-induced dehydration and the cryoprotection of cellular constituents. The quantification of soluble sugars in plant tissues is, therefore, essential in understanding freezing tolerance. While a number of analytical techniques and methods have been used to quantify sugars, most of these are expensive and time-consuming due to complex sample preparation procedures which require the derivatization of the carbohydrates being analyzed. Analysis of soluble sugars using capillary zone electrophoresis (CZE) under alkaline conditions with direct UV detection has previously been used to quantify simple sugars in fruit juices. However, it was unclear whether CZE-based methods could be successfully used to quantify the broader range of sugars present in complex plant extracts. Here, we present the development of an optimized CZE method capable of separating and quantifying mono-, di-, and tri-saccharides isolated from plant tissues. This optimized CZE method employs a column electrolyte buffer containing 130 mM NaOH, pH 13.0, creating a current of 185 μA when a separation voltage of 10 kV is employed. The optimized CZE method provides limits-of-detection (an average of 1.5 ng/μL) for individual carbohydrates comparable or superior to those obtained using gas chromatography-mass spectrometry, and allows resolution of non-structural sugars and cell wall components (structural sugars). The optimized CZE method was successfully used to quantify sugars from grape leaves and buds, and is a robust tool for the quantification of plant sugars found in vegetative and woody tissues. The increased analytical efficiency of this CZE method makes it ideal for use in high-throughput metabolomics studies designed to quantify plant sugars.

Greenhouse experiments were conducted at Wooster, OH, during 2010 and 2011 growing seasons to evaluate the responses of five wine grape cultivars to sublethal doses of 2,4-D, dicamba, and glyphosate, and the ‘Riesling’ grape to mixtures of 2,4-D plus glyphosate and dicamba plus glyphosate. Treatments were made using a spray system calibrated to deliver 0.757 L min−1at 276 kPa and 4.8 km h−1. Herbicides were delivered through 8002 flat spray nozzles and applied at 1/30, 1/100, and 1/300 of the recommended field rate of 840, 560, and 840 g ae ha−1for 2,4-D, dicamba, and glyphosate, respectively. Injury was observed in all treatments 7 d after treatment (DAT). However, injury symptoms greater than 10% were observed 42 DAT in plants treated with 2,4-D at all rates and plants treated with dicamba at the two highest rates. Injury (35%) at 357 DAT was noted only in plants treated with the highest rate of 2,4-D. French hybrids showed slightly less injury symptoms compared with wine grapes at 7 and 42 DAT. Shoot length reduction in plants treated with 2,4-D at the highest rate was 43, 84, and 16% at 7, 42, and 357 DAT, respectively. Glyphosate caused the fewest injury symptoms in Riesling compared with 2,4-D and dicamba when applied separately or tank mixed with glyphosate. Shoot length reduction in Riesling was observed 42 DAT with all rates of 2,4-D, with and without glyphosate and dicamba, and dicamba plus glyphosate at the highest rate; however, at 357 DAT, no effect was observed in shoot length. Spray drift of 2,4-D and dicamba can severely injure grapes, with injury increasing with increased exposure. The combination of 2,4-D plus glyphosate caused greater injury and shoot length reduction in grapes than glyphosate applied alone.

Plantings of Vitis vinifera L. cultivars have increased significantly in the eastern United States due to market demand for their wines. However, V. vinifera is a cold-sensitive species and planting new cultivars of unknown cold susceptibility in cold areas has resulted in frequent winter damage and crop loss. It is the purpose of this study to determine the freezing tolerance of 23 winegrape cultivars predominantly grown in Europe and South Africa and to compare three statistical methods [mode-date, piecewise regression, and annual mean LT50 (AFT)] for determining the minimum low temperature that will kill 50% of primary buds (LT50). Primary bud freezing tolerance (FT), expressed as LT50 in °C, was determined biweekly over three dormant seasons under field conditions in Ohio. Minimum LT50 was most accurately determined using the AFT method. AFT provided a lower error estimate than mode-date or piecewise regression and best corresponded with the percentage of vines that survived exposure to the polar vortex freeze events of 2014. The two-year average AFT ranged from −19°C for Gamay noir to −15°C for Barbera and distinguished a 1°C difference among cultivars in primary bud FT. We proposed to express cultivar AFT relative to a standard cultivar grown in the same location (Merlot in this study), termed RAFT. The results from this study can be used to assist selection of V. vinifera cultivars suitable for vineyard sites where freezing temperatures limit winegrape production.

Economic losses due to cold weather events are a major constraint to the expansion of premium but cold-sensitive winegrape cultivars in colder regions, such as Ohio (USDA) Plant Hardiness Zones 6b–5b (−17.8 to −26.1 °C) (ARS-USDA 2012). 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 'Pinot gris' grapevines (Vitis vinifera), and whether the effectiveness of ABA treatments can be influenced by the phenological timing of the application. Mature 'Pinot gris' grapevines were treated with a foliar application of ABA at a concentration of 0 mg L−1 (control), or 400 mg L−1 at vine phenological stages corresponding to véraison, post-véraison, and postharvest. ABA application did not affect yield components, fruit composition, or vegetative growth, but caused early leaf senescence, leaf abscission, and advanced dormancy that led to increased FT of 'Pinot gris' during the dormant season. The phenological timing of application influenced ABA effectiveness, with spray applications made at véraison and post-véraison being the most effective. It was concluded that a foliar application of ABA increased bud FT during the dormant season, and thus, ABA is a potential cultural practice tool for mitigating economic losses from cold injury in production regions with damaging cold events.

In this study, we characterized the influence of genotype and bud position on seasonal changes in freezing tolerance (FT, LT50) and soluble sugars, especially raffinose, and the affect of artificial deacclimation in buds of three field-grown cultivars over two years. Generally, basal buds were more freeze tolerant, and the cold-hardy cultivars Couderc 3309 (3309C; Vitis riparia x V. rupestris) and Concord (CD; V. labruscana) had the lowest LT50 compared to the cold-sensitive Cabernet franc (CF; V. vinifera). Among all sugars, fructose, glucose, sucrose, raffinose, and stachyose had strong correlation with LT50, but distinctive responses associated with bud position and cultivar were related to raffinose. Basal buds accumulated the most raffinose, and raffinose concentrations were two- to three-fold higher in the cold-hardy CD and 3309C than those in the cold-sensitive CF. Furthermore, CD and 3309C started accumulating raffinose with decreasing photoperiod prior to exposure to cold temperature, resulting in an early increase of FT. These results suggest that raffinose accumulation might be an early step in the process of cold acclimation that coincides with early development of FT. We concluded that bud raffinose concentration might be a useful detection tool and a metabolic marker during the early stages of cold acclimation to distinguish various Vitis genotypes with contrasting FT.

North American grapevine yellows (NAGY) disease has sometimes been attributed to infection of Vitis vinifera L. by Prunus X-disease phytoplasma ('Candidatus Phytoplasma pruni') but this attribution may not be fully adequate. In this study, phytoplasma strains related to 'Ca. Phytoplasma pruni' were found in NAGY-diseased grapevines in Maryland, Pennsylvania, Virginia, Ohio, Missouri, and New York State. Based on restriction fragment length polymorphism analysis of 16S ribosomal RNA gene (16S rDNA) sequences, the strains (termed NAGYIII strains) were classified in group 16SrIII (X-disease group) but they contained a recognition site for the restriction endonuclease MseI that is not present in the 16S rDNA of 'Ca. Phytoplasma pruni'. The 16S rDNA of the strains differed by three or four nucleotides from that of 'Ca. Phytoplasma pruni', indicating that they belonged to two novel 16S rDNA sequevars, designated NAGYIIIα and NAGYIIIβ. Both sequevars differed from 'Ca. Phytoplasma pruni' by a single base in each of three regions corresponding to species-unique (signature) sequences described for 'Ca. Phytoplasma pruni'. Phylogenetic analyses of 16S rRNA genes and SecY proteins, and single-nucleotide polymorphism analyses of secY and ribosomal protein genes, further distinguished the two grapevine sequevar lineages from one another and from 'Ca. Phytoplasma pruni'. The NAGYIIIα and NAGYIIIβ sequevars also differed from 'Ca. Phytoplasma pruni' in regions of the folded SecY protein that are predicted to be near or exposed at the outer surface of the phytoplasma membrane. No evidence indicated that diseased grapevines contained any phytoplasma strain conforming to 'Ca. Phytoplasma pruni' sensu stricto. Because the NAGYIII sequevars have not been reported in X-disease, a question is raised as to whether NAGYIII and Prunus X-disease are caused by different phytoplasma genotypes.

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.