Basal Leaf Removal Research Articles

Schwankungen im Gesamtgehalt an phenolischen-Verbindungen, Anthocyanen und Monoterpenen bei der Tafeltraubensorte (V. vinifera L.) ‘Muscat Hamburg’ als Ergebnis der Ausdünnung des Traubenbehanges und des frühen und späten Entfernens der basalen Blätter

Cluster thinning (CT) and basal leaf removal (BLR) are common canopy management practices used in grape growing. In recent years, novel viticultural techniques have been evolved all around the world to decrease costs of yield management, causing improvement in grape quality. The purpose of this study was to evaluate the effects of CT and early and late period BLR treatments on yield and quality components of cv. ‘Muscat Hamburg’. While BLR treatments were performing at pre-bloom (PB, early), berry set (BS), berries with pea size (PS), verasion (V), CT treatment was conducted at verasion period. Compared to Control, while the total phenolic compounds content, total anthocyanin content, free volatile terpenes content and potentially volatile terpenes content were made better by CT treatment and BLR treatments applied from berry set to verasion period gradually raised all these quality components.

Grape cluster microclimate influences the aroma composition of Sauvignon blanc wine

New Zealand Sauvignon blanc (SB) wines are characterised by a distinctive combination of tropical-fruity and green-herbaceous aromatic compounds. The influence of sunlight exposure of grape clusters on juice and wine composition was investigated, with the aim of manipulating aromatic compounds in SB wine. In the absence of basal leaf removal SB clusters naturally exposed to sunlight were riper than shaded clusters, evidenced by higher total soluble solids (TSS) and proline, and lower malic acid, 3-isobutyl-2-methoxypyrazine (IBMP) and arginine. Volatile thiols in wines did not differ between shaded and exposed clusters. At equivalent TSS, cluster exposure had little or no effect on malic acid concentration. Conversely, wine from shaded clusters had almost double the IBMP concentration of wine from exposed clusters at equivalent TSS. The effects on SB juice and wine composition of natural variations in cluster microclimate are not comparable with the effects of cluster exposure created through leaf removal.

CLUSTER THINNING EFFECTS ON THE FRUIT AND WINE QUALITY OF 'DOONURI' GRAPE

The quality of wine is influenced primarily by the quality of the raw material and secondly by fermentation technology. In general, important methods of cultivation for increasing the quality of the grape are shoot thinning, desuckering, shoot positioning and topping, basal leaf removal, girdling, cluster thinning and berry thinning. In this study the influence of cluster thinning was investigated to set standards for management for the grape cultivar ?Doonuri?. The ?Doonuri? grape was a cross of ?Schuyler? and ?Campbell Early? at the National Institute of Horticultural and Herbal Science in Korea in 2006. This red grape has a full fruit aroma, and it was used as a table and wine grape. In addition, this cultivar had a resistance to cold in winter as well as a downy mildew resistance. The fruit setting of grapes after cluster thinning was adjusted to 1.1 ton (1 cluster per shoot), 1.5 tons (1.5 clusters per shoot), and 2.1 tons (2 clusters per shoot) per 10 ares. As a result, ripening was faster when the yield was 1.5 t then 2.1 t per 10 are. Total acidity was reduced about 0.2% (w/v) at 1.5 t compared with 2.1 t. On the other hand, the sugar content was higher, about 2~3°Brix. The total acidity and sugar content for the 1.1 and 1.5 t levels were not significantly different. As cluster thinning increased, total polyphenol and total anthocyanin contents increased with early maturity. Also, the grapes with less 1.5 t per 10 acre were able to produce high quality wine.

Leaf removal and wine composition of Vitis vinifera L. cv. Nero d'Avola: the volatile aroma constituents.

Defoliation is a cultural practice for crop management in grapevines and the benefits effects have been demonstrated. Here, the influence of 'early' leaf removal on the quality of Nero d'Avola wines was evaluated. Particular attention has been given to the volatile constituents responsible for the wine aroma but also to the total amount of polyphenolic compounds, anthocyanins and flavonoids. 'Early' defoliation was manually applied and compared with non-defoliated controls. The grapes were harvested at two different ripening times following their technological and phenolic maturity. Statistical quantitative differences occurred among the samples from the four trials (defoliated and control samples, both at two ripening times). Both the time of harvest and the vine leaf removal determined variation in the wine composition. A large number of volatile constituents were identified and quantified; the odour activity values (OAVs) were calculated. Basal leaf removal reduced pH and increased titratable acidity, total amount of anthocyanins, flavonoids, polyphenols and colour intensity in the wines from the first harvest. Results showed the increase of fermentation and varietal aromas in the defoliated wines from the first harvest. Limited differences occurred between the wines from defoliated and control vines relative to the second harvest. Principal components analysis, which was applied to compounds with OAVs ≥ 0.5, allowed the different compounds to be distinguished. 'Early' leaf removal can lead to a positive effect on the quality of Nero d'Avola under the environmental conditions in which the present study was undertaken but particular attention has to be given to the time of grape harvest. The results also demonstrate that 'early' defoliation can be applied to improve wine quality in the Mediterranean region, where there is a concentration of rainfall during winter, and nearly arid conditions and high temperatures during the summer.

Interactions of summer pruning techniques and vine performance in the whiteVitis viniferacv. Ortrugo

Background and Aims The increasing interest by the wine market in sparkling white wines challenges how the desired grape composition can be achieved under the pressure of global warming. The aim of the present study was to assess the viability of summer pruning as a tool to pilot ripening towards desired compositional patterns. Methods and Results Ortrugo was subjected to basal leaf removal applied either at pre-flowering (ELR) or in lag-phase (LLR) and to bunch thinning (BT; removal of 50% of crop at lag-phase) in comparison with untreated control (C). Treatments induced large variation in bunch mass (30% less in ELR vs BT), yield per vine (37 and 21% less in BT and ELR vs C) and total soluble solids at harvest (BT scored 2.9°Brix higher than that of C). Conversely, given the same harvest date, all practices failed to maintain titratable acidity (TA) at the threshold of 6.5 g/L. Conclusions The data suggest that crop regulation achieved in the high yielding Ortrugo, through either BT or ELR, increases sugar accumulation rate so that concurrent optimal TA level (≅6.5 g/L) can be easily achieved by slightly anticipating harvest date. Under conditions of thermal or light stress, or weather conducive to bunch rot, preference should be given to ELR. Significance of the Study Suitable summer pruning techniques might be used as flexible and powerful tools to direct ripening towards the desired crop composition.

Effect of grape bunch sunlight exposure and UV radiation on phenolics and volatile composition of Vitis vinifera L. cv. Pinot noir wine

The effect of canopy leaf removal and ultraviolet (UV) on Pinot noir grape and wine composition was investigated in this study. Limited basal leaf removal in the fruit zone was conducted, compared to shaded bunches. The UV exposure was controlled using polycarbonate screens to block UV radiation, and acrylic screens to pass the UV. The results showed that bunch sunlight and UV exposure significantly increased the Brix and pH in the grape juice, and increased substantially wine colour density, anthocyanins, total pigment, total phenolics and tannin content. Bunch sunlight and UV exposure affected terpene alcohols, C13-norisprenoids and other volatile composition of the wine differently. Sunlight exposure and UV resulted in increase of nerol, geraniol and citronellol but not linalool. Sunlight exposure slightly increased the concentration of β-ionone, but the increase was not statistically significant for UV treatment. Neither sunlight nor UV treatment showed any impact on the concentration of β-damascenone.

Impact of Cluster Thinning and Basal Leaf Removal on Fruit Quality of Cabernet Franc (Vitis vinifera L.) Grapevines Grown in Cool Climate Conditions

Achieving desired fruit quality at harvest in cool climate conditions is a challenge, especially for red varieties, and the typical inability of fruit to reach technological maturity is a critical contributing factor requiring examination. To probe this issue, this research investigated the impact of two levels of crop thinning and of basal leaf removal at three phenological stages in the 2011 and 2012 growing seasons in Michigan. Experiments were conducted at the Southwest Michigan Research and Extension Center (SWMREC) in Benton Harbor. Using ‘Cabernet franc’ (Vitis vinifera L.) vines, yield components (yield per vine, pruning weight, and cluster and berry weight) and basic fruit composition traits [total soluble solids (TSS), pH, titratable acidity, anthocyanins, and phenolics) were studied to investigate the effect of cluster thinning and basal leaf removal on vine performance and fruit quality at harvest. Neither of the treatments significantly impacted TSS in either of the two seasons. Cluster thinning treatment successfully altered cropload ratio, indexed as Ravaz Index (RI), independently of the time of application. Basal leaf removal increased exposed berry temperature, cluster light exposure, and subsequent anthocyanin and phenolic content of the berry in both seasons, again independent of application date, whereas cluster thinning was effective only in 2012. Crop thinning coupled with basal leaf removal resulted in an increased efficiency in anthocyanin accumulation in relation to TSS accumulation, expressed as anthocyanin:sugar, in both years. This is significant because it offers potential for vineyard management practices aiming to improve fruit quality in cool climates where the onset of anthocyanin accumulation could be reduced and decoupled from sugar accumulation.

Effect of Severity of Leaf and Crop Removal on Grape and Wine Composition of Merlot Vines in Hawke’s Bay Vineyards

Manipulation of vine balance is widely practiced to enhance grape and wine quality. Reported benefits from crop thinning are ambiguous. Studies were undertaken over two growing seasons (2006–2008) in Hawke’s Bay, a cool-climate region of New Zealand, to investigate the influence of basal leaf and crop removal on fruit and wine composition and the indices of vine balance associated with optimum quality. Three levels of basal leaf removal in the fruiting zone were used. Crop removal achieved average reductions of 15% with moderate treatment and 35% with severe treatment below the average nonthinned yield of 17.5 t/ha. Treatments were undertaken at the preveraison growth stage on Merlot vines. Leaf removal had no effect on fruit composition, but levels of total anthocyanins and the flavonol quercetin-3-glucoside were enhanced in the wines. In contrast, crop removal increased sugar concentration and decreased titratable acidity of the must. While crop removal had no effect on wine anthocyanins, the proportions of anthocyanins as malvidin-3-glucosides and total phenolics in the wines were significantly increased. Relative to accepted indices of vine balance, the study vines were unbalanced with excessive shoot growth and dense canopies. A crop reduction of ~6.0 t/ha brought the capacity of the exposed leaf area into balance with that required to ripen fruit to optimum maturity and produce high-quality wines.

Impact of Prebloom and Fruit Set Basal Leaf Removal on the Flavonol and Anthocyanin Composition of Tempranillo Grapes

The influence of timing and method of basal defoliation on the profile and content of anthocyanins and flavonols in Tempranillo grapes was investigated. Basal leaf removal was manually and mechanically performed at two phenological stages, prebloom and fruit set. Phenolic composition was determined in grape extracts by HPLC-UV-Vis and 13 anthocyanin and flavonol compounds were identified and quantified. Regardless of the timing and method of defoliation, basal leaf removal led to more ripened fruit in terms of higher soluble solids and reduced acidity and favored the accumulation of flavonols and anthocyanins, which was related to the increase in total leaf area per yield observed in defoliated vines. For anthocyanins, there was a significant relationship between their concentrations and the larger relative skin mass observed in berries of defoliated vines. In general, the enhancement in flavonols and anthocyanins observed in berries from basal-defoliated vines tended to be greater when defoliation was conducted mechanically; yet overall, no evident differences between prebloom and fruit-set defoliation were found.

Basal defoliation and their influence in agronomic and phytopathological traits in tomato plants

The incidence of leaf diseases is one of the main factors limiting the tomato crop production, increasing the production cost due to excessive pesticide application. The basal leaf removal could reduce inoculum sources, disease severity and contribute to reducing the use of pesticide. Aiming to evaluate the efficiency of this practice on the reduction of tomato leaf diseases and the effect in the quality and in the productivity of the tomato plants for in natura consumption, two experiments were carried out to test four levels of basal leaf removal. Basal leaves removal, at fruit harvesting, is efficient in reducing the infected plant area by disease, what can mean smaller disease severity and least inoculum source in the field. Also, the all basal leaf removal does not affect yield and quality of the tomato fruits. Other studies are necessary to evaluate the effect of adopting this practice in different planting dates, spacing, varieties, successive plantings and the financial viability of adopting this practice.

Canopy Management and Enzyme Impacts on Merlot, Cabernet franc, and Cabernet Sauvignon. II. Wine Composition and Quality

Merlot, Cabernet franc, and Cabernet Sauvignon vines in Niagara-on-the-Lake, Ontario, were subjected to four treatments in a randomized complete block experiment: hedged control, cluster thinning at veraison (CT), basal leaf removal (BLR), and CT+BLR. Musts from each treatment replicate (CT+BLR excepted) were thereafter either left untreated or treated with one of ColorPro or Color X enzymes. In most cases, CT and CT+BLR treatments had the highest wine anthocyanin and phenol concentrations and the highest color intensities (A₄₂₀ + A₅₂₀). Leaf removal resulted in small increases in wine color intensity and anthocyanin and phenol concentrations. Cluster thinned and BLR treatments both reduced titratable acidity (TA) and increased pH relative to controls, but BLR tended to be more effective than CT. The CT+BLR treatments usually resulted in the lowest TA and the highest pH. Enzyme treatments increased wine TA and reduced pH and typically increased color intensity, total anthocyanins, and phenols. Both viticultural and enological treatments had noteworthy impacts on individual wine phenolic compounds and anthocyanins, although the viticultural treatments were more efficacious. The viticultural treatments enhanced intensities of several aroma and retronasal descriptors (e.g., black fruit, black pepper, tobacco) and reduced those of others (e.g., bean/pea, mushroom). The CT+BLR treatment has the potential to substantially improve fruit and wine composition in cool-climate regions; negatively, excessive leaf removal could result in lowered ethanol and undesirable increases in pH. Enzyme treatment has the potential for increased color intensity, but with occasional increases in TA.

Impact of Severity and Timing of Basal Leaf Removal on 3-Isobutyl-2-Methoxypyrazine Concentrations in Red Winegrapes

Field studies were conducted on <i>Vitis vinifera</i> L. cvs. Cabernet franc and Merlot to evaluate the effects of basal leaf removal timing and severity on 3-isobutyl-2-methoxypyrazine (IBMP) concentration in grape berries. Treatments consisted of removing either 50% or 100% of leaves from the fruiting zone at either 10 days after anthesis, 40 days after anthesis, or 60 days after anthesis. In the second year of the Cabernet franc study, a 15-day postveraison leaf removal treatment was also included. In both years of the Cabernet franc study, significant reductions in IBMP (range = 28 to 53%) were observed before veraison compared with the control in both 10 days after anthesis treatments (50% and 100% leaf removal). In 2007, all leaf removal treatments significantly reduced IBMP concentrations compared with the control (46 to 88%) in Cabernet franc berries at harvest, with the greatest reduction observed in the 100% leaf removal treatments at 10 days after anthesis and 40 days after anthesis. In 2008, the 100% leaf removal treatment at 10 days after anthesis and the 50 and 100% leaf removal treatments at 40 days after anthesis significantly reduced IBMP concentrations (34 to 60%) in mature Cabernet franc berries. In the Merlot trial, all leaf removal treatments significantly reduced IBMP concentrations (38 to 52%) at harvest. In summary, early season (10 to 40 day after anthesis) basal leaf removal reduced IBMP accumulation preveraison compared with the control in both studies, suggesting that early leaf removal is a more effective management strategy to reduce IBMP accumulation in grape berries than leaf removal later in the season.

A three-year survey on the impact of pre-flowering leaf removal on berry growth components and grape composition in cv. Barbera vines

&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Aims&lt;/strong&gt;: Competitiveness in modern viticulture requires that vineyard management techniques used for crop regulation, besides being economically viable, would assure stable grape composition improvement across variability of genotypes and seasons. Pre-flowering basal leaf removal has previously been shown as an effective tool in controlling yield primarily through a reduced fruit-set. This study aims to evaluate the impact of early leaf removal on the differential growth of the various berry organs (skin, flesh and seeds) as well as the constancy of such effects across season variability and their impact on final grape composition.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Methods and results&lt;/strong&gt;: Pre-bloom defoliation (D) of the first six basal leaves on main shoots was applied to the field-grown Barbera cultivar (&lt;em&gt;Vitis vinifera&lt;/em&gt; L.) from 2006 to 2008 and compared with non-defoliated (ND) controls. Over a three-year period, defoliation induced a 34% average reduction in berry number as compared to ND, which led to a notable decrease in fruit-set (-7.6 %), cluster mass (-34%) and yield per shoot (-30%). The berry mass showed a significant relationship with the year factor, as berry size in D shoots was larger, similar and smaller than ND in 2006, 2007 and 2008, respectively. In both treatments, skin mass was closely correlated with berry mass and, within each season and berry mass category, D had relative skin mass values higher than ND. Although the effects were milder in 2007, D induced a significant increase in soluble solids, anthocyanins and phenolics, whereas total acidity was unaffected.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Conclusion&lt;/strong&gt;: These results indicate that, regardless of final berry size, a pre-flowering defoliation favors skin development, which results in higher relative skin mass than ND vines. This effect appears to predominate over variations due to specific weather and cultural conditions along the season and leads to a marked improvement in final grape composition.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Significance and impact of study&lt;/strong&gt;: Repeatability of results implies a strong physiological regulation of this technique and encourages extension of its use in areas where the occurrence of high cropping and large clusters with a high degree of compactness does exist. In a global warming scenario, it is also relevant that the yield decrease and the improvement in overall grape composition are not obtained at the expense of a further reduction in berry acidity.&lt;/p&gt;

Composition and Wine Sensory Attributes of Chardonnay Musqué from Different Viticultural Treatments

ABSTRACT ‘Chardonnay Musqué’ vines in Beamsville, Ontario, were subjected in one trial to three treatments: (1) control (hedged only); (2) basal leaf removal (BLR) and cluster thinning and; (3) cluster thinning during five stages of berry development. Berries and musts from each treatment were analyzed for soluble solids (Brix), pH, titratable acidity (TA), as well as free and potential monoterpenes (FVT and PVT). Wines produced from each treatment were evaluated by descriptive analysis for aroma and flavor intensities. FVT and PVT of berries were higher in thinned vines compared to non-thinned vines. Cluster thinning at veraison yielded fruit with the highest FVT and PVT concentrations. Leaf-pulled vines produced fruit with increased pH, reduced TA and highest FVT and PVT. Wines from BLR and thinning treatments generally had higher muscat and floral/perfumy aromas, and could be separated based on overall quality. The chemical and sensory data were incorporated into a multiple regression model used to construct a grape quality model for aromatic white Vitis vinifera grape cultivars in the Niagara Peninsula. The model developed was able to predict overall quality based on Brix, pH, and berry FVT and PVT concentration. The model was partially validated by correlations between berry FVT and PVT vs. floral and muscat aromas in wines from three previous vintages. This model has potential for use to create a more equitable payment schedule for growers contracted to wineries for the purchase of high-quality grapes.

Magnitude and Interaction of Viticultural and Enological Effects. I. Impact of Canopy Management and Yeast Strain on Sensory and Chemical Composition of Chardonnay Musqué

Chardonnay Musqué vines in Ontario were subjected to hedging (control), basal leaf removal (BLR), or cluster thinning (CT) over a 3-year period. Musts from each treatment were combined in a factorial treatment arrangement with yeast strains VL1, EC1118, and EC1118 + enzyme preparation AR2000. Yield was reduced by 21 to 36% by CT as a result of cluster removal. Fruit maturity was advanced by BLR and CT in reduced berry, must, and wine titratable acidity (TA); increased berry and must pH and Brix; increased must and wine free volatile terpenes (FVT) (CT only); and increased berry, must, and wine potentially volatile terpenes (PVT). VL1 wines were lower in pH and both FVT and PVT (1 of 3 years) than those of EC1118 and had higher TA (1 of 3 years). EC1118 + AR2000 wines did not differ from wines produced solely with EC1118 in terms of TA and FVT but were higher in PVT and pH. CT wines differed from BLR and control wines sensorially, with increased depth of color, higher sweetness and herbaceous/grassy aroma, and reduced tropical fruit aroma. BLR wines had higher tropical fruit and floral aromas, while control wines had greater acidity. Principal component analysis of sensory data suggested that variation in wine sensory profiles was due to both viticultural and enological practices.

Gibberellic Acid and Basal Leaf Removal: Implications for Fruit Maturity, Vestigial Seed Development, and Sensory Attributes of Sovereign Coronation Table Grapes

Bloom (20 mg/L) and various postbloom (40 to 100 mg/L) applications of gibberellic acid (GA) ± basal leaf removal (BLR) were imposed on Sovereign Coronation vines over a three-year period. GA increased yield in one of three years and berry weight in all three years, while vestigial seed development decreased in two of three years as a linear function of the concentration of GA applied. Brix was reduced linearly with increasing GA in two of three years, pH was generally unaffected, but titratable acidity decreased with increasing GA. Color intensity and anthocyanins increased relative to GA in 2002 only. Methyl anthranilate increased relative to GA in one season while total volatile esters also increased with increasing GA. Treatments involving 40 mg/L GA led to higher fruity and labrusca flavor, sweetness, persistence of flavor, and overall impression, as well as lower acidity and bitterness. Basal leaf removal delayed berry maturity slightly but increased light penetration into the canopy. Berries from non-GA-sprayed control treatments ± BLR were separated into several maturity categories (based on berry Brix) by sucrose buoyant density gradients and were thereafter subjected to sensory evaluation. Increased berry maturity was associated with decreased berry weight and titratable acidity, and increased color intensity, anthocyanins, phenols, methyl anthranilate, and total volatile esters. Principal component analysis coupled with discriminant analysis suggested that soluble solids ≥17 Brix was associated with sweetness, fruity, labrusca, and overall impression.

Impact of Training System, Vine Spacing, and Basal Leaf Removal on Riesling. Vine Performance, Berry Composition, Canopy Microclimate, and Vineyard Labor Requirements

Own-rooted Riesling vines were subjected, over a five-year period, to five training treatments [alternate double crossarm (ADC); Lenz Moser (LM); low cordon (LC); low-V (LV); pendelbogen (PB)] and three within-row vine spacings (1.4, 1.8, and 2.4 m), with and without basal leaf removal applied to one-half of each vine at approximately 45 days post-bloom. Weight of cane prunings (vine size) was nearly optimal in ADC, LM, and PB systems, but was excessive in the other two training treatments. Increased vine spacing decreased vine size linearly on a per meter of row basis. Canopy density was optimized by ADC and PB training, and these two systems also had the least number of shaded leaves. Both ADC and LV systems tended to have the greatest number of exposed clusters. Yields of divided canopies (ADC and LV) averaged 55% higher than single curtain systems, but cluster weights were lower, and ADC berry weights were also lower. The ADC system produced fruit with lowest °Brix, but also with lowest titratable acidity (TA) and pH, and highest free volatile terpene (FVT) and potentially-volatile terpene (PVT) content. Leaf removal consistently reduced TA, canopy density, and shaded leaves, and significantly increased cluster exposure, FVT, and PVT. Vine spacing had a limited influence on yield and fruit composition, but interacted with training system and leaf removal on some components. ADC training led to higher leaf and cluster exposure, and higher cluster temperatures than LC training, with little difference in transpiration rate and leaf water potential. Labor requirements per m of canopy were lowest in ADC vines.

Vine Performance, Fruit Composition, and Wine Sensory Attributes of Gewürztraminer in Response to Vineyard Location and Canopy Manipulation

An experiment was conducted on Gewürztraminer vines between 1988 and 1992 in the Okanagan Valley of British Columbia, Canada, to assess the impact of three canopy manipulation practices (unhedged control; hedged to <i>ca.</i> 14 leaves per shoot; basal leaf removal) at each of three vineyard sites [Oliver (Region II); Kaleden (Region I/II); Kelowna (Region I)]. The Kelowna site was characterized by lowest weight of cane prunings and canopy density, and highest cluster weight and number of berries per cluster. Site had no consistent effect on berry and juice °Brix, but highest pH, potassium (K⁺), free volatile terpenes (FVT) and potentially-volatile terpenes (PVT), and lowest titratable acidity (TA) were measured at the Oliver site. Basal leaf removal lowered °Brix, TA, pH, and K⁺,and increased FVT and PVT in the berries and juices in some years. In triangle tests, tasters could discern between some pairs of sites and canopy manipulation treatments on an aroma and retronasal aroma (hereinafter known as flavor) basis, and found in most cases that leaf removal wines had highest muscat and floral aromas and flavors. Descriptive analysis of wine sensory attributes showed that the Oliver site, and the hedging and leaf removal treatments, contained most intense fruity, muscat, and cedar aromas and flavors, as well as most body and aftertaste.

Population dynamics of epiphytic mycoflora and occurrence of bunch rots of wine grapes as influenced by leaf removal

Population dynamics of epiphytic fungi associated with the summer bunch rot complex of five wine grape (Vitis vinifera) varieties in commercial vineyards in the San Joaquin Valley of California were monitored every two weeks by berry washings during 1989‐1992. Vines in the five replicated experiments were subjected to basal leaf removal or left unaltered. Although numerous genera of fungi were isolated, species of Cladosporium, Aspergillus, Penicillium and Alternaria predominated. Population densities of most fungal taxa increased at or after véraison. Leaf removal in the fruiting zones of bilateral cordon‐trained vines generally reduced (P &gt;0·05) mid to late season numbers of epiphytic mycoflora: species of Penicillium, Botrytis and Aspergillus were most commonly reduced. Populations of Alternaria spp. and yeasts were not consistently affected by leaf removal. Numbers of fungi were no lower on berries when leaves were removed from both sides of vines than when leaves were removed only from the shaded side. Incidence and severity of bunch rots (sour rot, rots caused by Botrytis cinerea, Aspergillus niger, and total rot) at harvest were consistently reduced where leaves had been removed in comparison to vines where no leaves were removed. In one experiment, berries from vines sprayed with the grower's choice of pesticides at 50% or 100% of label rates had similar numbers of epiphytic mycoflora in both cases frequently lower than those from unsprayed controls. There was a significant interaction between chemical rate and leaf removal on the incidence of sour rot at harvest. Timing and extent of leaf removal did not affect population dynamics of epiphytic fungi, or incidence or severity of bunch rots (P≤0·05) at harvest in other trials.

Leaf removal improves fungicide control of powdery mildew in SJV grapes

Basal leaf removal, which has been used to reduce damage from bunch rots and seasonal leafhopper infestations, was tested for its effects on powdery mildew in the San Joaquin Valley. Powdery mildew is one of the most damaging diseases of wine grapes in California. On-farm experiments showed that leaf removal reduced the disease in two of five experiments and facilitated improved spray coverage in grapevine fruiting zones. Leaf removal can improve the effectiveness of fungicide programs in reducing powdery mildew damage, but should not be relied upon alone to control the disease.