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Background and Aims Postveraison limitation of canopy photosynthesis delays grape berry ripening and reduces sugar accumulation, thus lowering the alcohol content of the subsequent wines. This study was designed to evaluate whether similar results could be obtained by defoliation apical to the bunch zone using a leaf‐plucking machine when berry sugar content was approximately 16–17°Brix. Methods and Results In 2011 and 2012, defoliation treatments were applied postveraison to cv. Sangiovese vines (D) on either side of each row using a mechanical leaf remover, and these D vines were compared to a nondefoliated control (C). The machine removed 35% of the leaves on the vine and created a 50‐cm vertical window without leaves above the bunch area, but retained a few leaves at the canopy apex (about 0.50 m2/vine). In both years, leaf removal reduced the rate of berry sugar accumulation and led to a 1.2 lower harvest °Brix and consequently, a lower wine alcohol (−0.6%) content in D relative to that of C vines. In 2012, sugar content of D vines, monitored in a group of vines that was not harvested, had recovered to that of C vines 2 weeks after harvest. The concentration of total phenolic compounds in the grapes, the chemical and chromatic characteristics of the wines and the replenishment of soluble sugars, starch and total nitrogen in the canes and roots were similar in the D and C vines. Conclusion To achieve an effective delay in sugar accumulation in the berries, leaves should be removed at 16–17°Brix, and at least 30–35% of vine leaf area should be removed. Significance of the Study Mechanical removal of leaves postveraison above the bunch zone of Sangiovese can be an easy and economically viable technique for delaying sugar accumulation in the berries and for limiting the alcohol content of wines with no negative impact on desirable composition of either berries or wines.

Background and Aims:In recent years, increasing summer temperature, coupled with reduced and erratic rainfall during the growing season, has induced accelerated fruit ripening in several regions, resulting in an undesirable increase in wine alcohol concentration. This study was designed to evaluate the impact of canopy and water management on grape sugar and flavonoid accumulation, with the goal of reducing wine alcohol concentration while conserving or enhancing the concentration of phenolic substances. Methods and Results: In 2011 and 2012, two irrigation treatments (I -irrigated and DI -deficit irrigated) and two canopy heights (HC -high canopy and SC -short canopy) were applied in a Merlot vineyard. No interactions between treatments were observed, and thus independent results were obtained; DI berries had significantly higher sugar concentration (+5%) than that of I in both years and higher wine alcohol concentration only in 2012. Short canopy berries had lower sugar concentration (−4%) and lower wine alcohol (−8%) (only in 2011) than that of HC. Anthocyanins and tannins in berry and wine were increased by water deficit and not affected by severe trimming. Conclusions: Deficit irrigation did not reduce berry sugar concentration and wine alcohol concentration but did enhance desirable wine attributes. Berry sugar concentration and alcohol concentration in wine were reduced by SC in one of the two seasons. Water deficit and severe trimming showed independent effects on berry composition. Significance of the Study: Severe canopy reduction at early stages of ripening can reduce sugars without affecting the accumulation of anthocyanins in Merlot. Conversely, DI applied before veraison, despite promoting anthocyanins accumulation, may also increase berry sugar concentration at harvest.

Abstract:The effectiveness of a postveraison application of the film-forming antitranspirant Vapor Gard (VG, a.i. di-1-p-menthene) was investigated as a technique to delay grape ripening and reduce sugar accumulation in the berry. The study was carried out over the 2010-2011 seasons in a nonirrigated vineyard of cv. Sangiovese in central Italy.Vapor Gard was applied at 2% concentration to the upper two-thirds of the canopy (most functional leaves) and it significantly lowered leaf assimilation and transpiration rates and increased intrinsic water use efficiency. The F v / F m ratio was not modified, emphasizing that photoinhibition did not occur at the photosystem II complex, whereas the reduction of pool size of plastoquinone matched well with reduced CO 2 fixation found in VG-treated vines. In both years VG treatment reduced the pace of sugar accumulation in the berry as compared to control vines, scoring a -1.2 Brix at harvest and wine alcohol content at -1% without compromising the recovery of concentrations of carbohydrates and total nitrogen in canes and roots. Concurrently, organic acids, pH, and phenolic richness of grapes and wines were unaffected, whereas there was a decrease in anthocyanin content in the berry (-19% compared to control vines) and in the wine (-15% compared to control vines). The application of VG at postveraison above the cluster zone is an effective, simple, and viable technique to hinder berry sugaring and obtain less alcoholic wines.To be effective the spraying should be performed at ~14 to 15 Brix, making sure that the lower leaf epidermis is fully wetted by the chemical.

ABSTRACT:The development and accumulation of secondary metabolites in grapes determine wine color, taste, and aroma. This study aimed to investigate the effect of leaf removal before flowering, a practice recently introduced to reduce cluster compactness and Botrytis rot, on anthocyanin, tannin, and methoxypyrazine concentrations in 'Merlot' grapes and wines. Leaf removal before flowering was compared with leaf removal after flowering and an untreated control. No effects on tannin and anthocyanin concentrations in grapes were observed. Both treatments reduced levels of 3-isobutyl-2-methoxypyrazine (IBMP) in the grapes and the derived wines, although the after-flowering treatment did so to a greater degree in the fruit specifically. Leaf removal before flowering can be used to reduce cluster compactness, Botrytis rot, and grape and wine IBMP concentration and to improve wine color intensity but at the expense of cluster weight and vine yield. Leaf removal after flowering accomplishes essentially the same results without loss of yield.

Viticulture in Michigan is limited by a cool and humid climate and as a result, there is a problem of harvest season cluster rot, especially in cultivars with compact cluster morphology. Economically important wine grape varieties in eastern North America possess varying susceptibility to harvest season cluster rot. Some important cultivars that are susceptible are Pinot gris, Pinot noir, Riesling (Vitis vinifera L.) as well as Seyval and Vignoles (French–American hybrids or interspecific hybrid cultivars). A common characteristic of these cultivars is the compactness of the berries held on the cluster rachis. The aim of this work was to determine whether a quantified amount of leaf removal or a temporary reduction in carbon assimilation at the beginning of bloom would reduce fruit set and cluster compactness. Vines subjected to removal of four or six basal leaves had an average fruit set reduction of ≈45% from a non-treated control. Cluster weight and berries per cluster were similarly reduced with a greater effect on the basal than the apical cluster of the shoot. Reduced fruit set was associated with a reduction in cluster compactness and harvest season rot. This was also reflected in yield and basic fruit chemistry parameters associated with the importance of basal leaves to the developing cluster. Multiple applications of stylet oil at different time intervals resulted in significant reduction in net photosynthesis (Pn). A single application had no significant impact on Pn, whereas multiple applications reduced leaf assimilation rates. However, this reduction in Pn did not reduce fruit set or improve cluster compactness. There was a strong negative effect of early leaf removal in Year 1 on vine performance in Year 2; this carryover effect increased shootless nodes per vine, reduced the number of clusters per shoot and per vine, and dramatically reduced fruit set and consequently yield per vine.

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Removal of basal leaves near blooms inevitably affects grapevine balance and cluster microclimate conditions, improving fruit quality. Mechanization of this practice allows growers to save time and resources, but to our knowledge, it has not yet been compared with the manual application of this practice in a cool-climate region where seasonal temperatures frequently limit fruit technological maturity and phenolic ripening in red Vitis vinifera cultivars. In our research, berry sugar concentration was highest with prebloom mechanical treatment (PB-ME). Furthermore, metabolomics analysis revealed that PB-ME favored the accumulation of significantly more disubstituted anthocyanins and flavonols and OH-substituted anthocyanins compared with manual application. Given that vine balance was similar between treatments, increased ripening with PB-ME is likely due to enhanced microclimate conditions and higher carbon partitioning through a younger canopy containing basal leaf fragments proximal to fruit. This information provides an important strategy for consistently ripening red Vitis vinifera cultivars in cool climates.