Timing Of Leaf Removal Research Articles

Cluster Zone Leaf Removal Reduces the Rate of Anthracnose (Elsinöe ampelina) Progress and Facilitates Its Control.

Anthracnose caused by Elsinöe ampelina is an economically important disease that affects certain hardy and semihardy grapevine cultivars. The control of this disease requires repeated application of fungicides, which has financial and environmental consequences. In this study, leaf removal in the cluster area was studied with a view to facilitating integrated anthracnose management. First, the effect of leaf removal timing (BBCH stage 53 or 71) and intensity (one or both sides of rows) on the progression of anthracnose and on the microclimate was studied in plots planted with Vidal blanc (Vitis vinifera) at two sites in both 2020 and 2021. Overall, at both sites and in both years, anthracnose on leaves was more severe in plots without cluster zone leaf removal. Regardless of the timing of leaf removal, anthracnose severity on leaves and incidence of infected berries at harvest were significantly lower in plots where leaves had been removed on both sides of the rows compared with plots where leaves were removed on one side only. Second, anthracnose management programs with leaf removal, with or without disease risk estimation, were evaluated. All anthracnose management programs including leaf removal in the cluster zone reduced anthracnose development compared with the standard program without leaf removal. Overall mean leaf anthracnose severity, severity at harvest, and anthracnose incidence on clusters at harvest were lower in plots with leaf removal than in the standard program, but the differences between the two treatments were not significant (P > 0.05). More fungicide applications were made in plots managed using the standard programs, specifically 13 applications, compared with plots managed based on assessing the weather-related risk of anthracnose, with 9 and 10 applications made at sites 1 and 2 for the risk-based program, respectively, and 5 and 7 applications made at sites 1 and 2, respectively, when microclimate within the cluster zone was considered. The results of this study clearly show the important role that leaf removal can play in managing grape anthracnose.

Timing of leaf removal modulates tannin composition and the level of anthocyanins and methoxypyrazines in Pinot noir grapes and wines

This study aimed to investigate the impact of leaf removal on concentrations of anthocyanin, tannin, and methoxypyrazines (MPs) in Pinot noir grapes and wines. Leaf removal after 7 days (LR7), 30 days (LR30), and 60 days (LR60) of flowering were compared with no leaf removal control (LRC). Grapes and resultant wines were analysed for tannin and aroma composition using liquid chromatography and two-dimensional gas chromatography–mass spectrometry. All leaf removal treatments increased anthocyanin concentration in grapes and reduced MP levels in grape stems compared to LRC, indicating the effectiveness of both early and late leaf removal. Leaf removal after 7 days and 30 days were more effective in enhancing colour density, polymeric pigments, and tannin concentration in wines. Higher grape skin tannin and anthocyanin concentrations, along with lower seed tannin concentration in berries, correlated with higher tannin concentrations in wines. LR7 showed significantly higher skin-originated tannin proportion than LRC, suggesting a useful tool to manage tannin extraction. Aroma composition of resultant wines was influenced by leaf removal, although these differences were not evident in the sensory evaluation.

Performance of Early Fruit-Zone Leaf Removal in Cabernet Sauvignon and Merlot in an Arid Climate

<h3>Summary</h3> <h3>Goals:</h3> Our goals were to evaluate how the timing of early fruit-zone leaf removal, done between prebloom and post-fruit set, influenced the risk of reduced fruit set, sunburn, and fruit quality in <i>Vitis vinifera</i> Cabernet Sauvignon and Merlot grown in the hot, arid, and irrigated region of eastern Washington State. <h3>Key Findings:</h3> Fruit set was reduced in <i>V. vinifera</i> Cabernet Sauvignon when fruit-zone leaf removal was completed during bloom. Prebloom and postbloom fruit-zone leaf removal did not reduce fruit set. Sunburn occurred on fruit on the westside of the canopy in both <i>V. vinifera</i> Cabernet Sauvignon and Merlot. Sunburn severity increased with later-timed fruit-zone leaf removal. Overall, the maximum severity of sunburn was 15% of the cluster surface area. Vintage had a greater effect on fruit quality than timing of leaf removal for both varieties. This emphasizes the need to make canopy management decisions that are informed by weather forecasts to achieve desired management goals. <h3>Impact and Significance:</h3> Early fruit-zone leaf removal was traditionally avoided in eastern Washington, in favor of completing the practice after berries have reached pea-size. The later timing of leaf removal, however, can result in sudden exposure of the fruit during the typically warmest and sunniest time of the growing season. Results from this study show that many of the assumed risks associated with early fruit-zone leaf removal, such as extreme reduction in fruit set and sunburn, are not fully realized. This means that early fruit-zone leaf removal could be adopted in this hot, arid climate without a high risk of reduction in fruit quantity or quality.

Early Defoliation Impact on Fruitset, Yield, Fruit Quality, and Cold Hardiness in ‘Chambourcin’ Grapevines

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.

Effects of leaf removal on grape cluster architecture and control of Botrytis bunch rot in Sauvignon Blanc grapevines in Southern Brazil

Management practices, such as leaf removal, can affect grape cluster architecture and the microclimate around the cluster, which influences the development of Botrytis bunch rot disease. The timing of leaf removal among five different phenological stages was investigated as a tool for managing grape cluster architecture-related variables and for managing Botrytis bunch rot of Sauvignon Blanc grapevines. A commercial vineyard located in São Joaquim municipality, in the highland region of Santa Catarina State, Southern Brazil, was assessed in a randomized complete block design during the 2015 and 2016 growing seasons. The treatments consisted of leaf removal of four basal leaves around clusters at the phenological stages of full bloom, buckshot berries, pea-sized berries, veraison, and 15 days after veraison. At harvest, cluster architecture variables (cluster length, cluster mass, rachis mass, number of berries, berry mass, and cluster compactness index) and Botrytis bunch rot incidence and severity were assessed weekly from the first appearance of symptoms to harvest. Disease progress curves were constructed and compared to several epidemiological parameters. There was no significant effect of the removal of four basal leaves on the cluster architecture-related variables (cluster and berry masses, number of berries, and cluster compactness index); however, reduced the intensity of Botrytis bunch rot. Leaf removal carried out before veraison significantly reduced (P < 0.05) the incidence, severity, AUDIPC, and AUDSPC of Botrytis cinerea in Sauvignon Blanc when compared with those of vines without leaf removal. Early leaf removal at the phenological stages of full bloom, buckshot berries, and pea-sized berries reduced the severity of B. cinerea infection and showed in the phenological stage of full bloom the lowest values for AUDSPC of 199.26 and 171.30 in the 2015 and 2016 growing seasons, respectively. The results of this study suggest that leaf removal carried out before veraison during the phenological stages of full bloom, buckshot berries, or pea-sized berries should be recommended for Sauvignon Blanc cultivar production to reduce Botrytis bunch rot in the highland regions of Santa Catarina State, Southern Brazil.

Effects of the severity and timing of basal leaf removal on the amino acids profiles of Sauvignon Blanc grapes and wines

The effects of the severity and timing of leaf removal (LR) on the amino acids of Sauvignon Blanc grapes and wines were studied during the 2017 growing season. High-performance liquid chromatography (HPLC) was used to analyze the amino acids profiles of grape berries and wines. The basal leaves were removed at three time points (40, 56 and 72 days after flowering, named LR40, LR56 and LR72, respectively) at two severity levels (one at which the first, third, and fifth basal leaves of each shoot were removed (50% level); and another at which the first six basal leaves were removed (100% level)). The results showed that leaf removal had little impact on total soluble solids (°Brix), titratable acidity, pH or berry weight. The LR72-50% treated grapes had higher berry weight, titratable acidity and °Brix than those of the other treatments. The highest concentrations of total amino acids and of total amino acids except proline were detected in LR72-50% treated grapes (2 952.58 and 2 764.36 mg L−1, respectively); the lowest were detected in LR72-100% treated grapes (2 172.82 and 2 038.71 mg L−1, respectively). LR72-50% treatment significantly promoted the synthesis of aspartic acid, serine, arginine, alanine, aminobutyric acid and proline at both severity levels for grapes, the concentrations of all of these amino acids were increased relative to the control concentrations. The LR72-50%, LR40-100% and LR72-100% treated wines had higher total amino acids concentrations and higher concentrations of some individual amino acids, such as arginine, alanine and serine, than did the control wines. Of all the amino acids studied, glycine, tyrosine, cysteine, methionine and lysine were not significantly influenced by the timing or severity basal defoliation in grapes and wines. The present study reveals the effects of the timing and severity of leaf removal on the amino acids profiles of grapes and wines.

The Effect of Partial Defoliation, Leaf Position and Developmental Stage of the Vine on Leaf Chlorophyll Concentration in Relation to the Photosynthetic Activity and Light Intensity in the Canopy of Vitis vinif era L. cv. Cabernet Sauvignon

The effect of partial defoliation and leaf position on leaf chlorophyll concentration in relation to the photosynthetic activity and light intensity in the canopy of Vitis vinifera L. cv. Cabernet Sauvignon was investigated at berry set, pea size, veraison and ripeness stages. The leaves of the severely defoliated vines appeared to contain the highest chlorophyll concentration. In general, chlorophyll a decreased as the leaves were situated progressively deeper into the canopy. No consistent relationship between chlorophyll concentration, light intensity and photosynthetic activity could be found for the different leaf positions. However, to obtain leaves that photosynthesize optimally, the amount and time of leaf removal in the grapevine canopy must be carefully planned.

Timing of leaf removal modifies chemical and phenolic composition of Sauvignon Blanc wine

The objective of this work was to evaluate the effect of different defoliation times on the chemical and phenolic composition of Sauvignon Blanc wine in high altitude regions of Santa Catarina - Brazil. The experiment was conducted in the 2015 and 2016 seasons, in a vineyard located in the city of Sao Joaquim – Santa Catarina State. The defoliation was carried out during phenological stages: full bloom, berries pepper-corn size, pea-sized berries, veraison, 15 days after veraison and control without leaf removal. During harvest, severity of Botrytis cinerea was assessed by visual evaluation through a diagrammatic scale. For the wine samples from each season, total acidity (meq L−1 ), pH, total polyphenol content (mg L−1 of gallic acid) and color (Abs 420nm) were performed. For the wines of the 2015 harvest, phenolic compounds were analyzed: gallic acid, catechin, vanillic acid, P-coumaric acid and rutin. The chemical composition of Sauvignon Blanc wine was affected as a result of leaf removal timing, defoliation carried out in full bloom, berries pepper-corn size and pea-sized berries reduced total acidity and increased pH of the wines in both seasons. For wine color, in both seasons, it was found a greater yellow coloration in wines originated from grapes where the plants were not defoliated. The increase of yellow coloration is due to the oxidation of catechins and epicatechins, which is related to the increase of botrytis bunch rot. In the 2015 season there were no influence of leaf removal timing in total polyphenols, however, in the 2016, the defoliation performed in full bloom resulted in lower polyphenols contents. Wines from non-defoliated plants presented higher values of catechin, rutin, P-coumaric acid and gallic acid, related to yellow coloration of wines and greater susceptibility to darkening and oxidation. For vanillic acid, wines from non-defoliated plants have the lowest values, this compound is important in wine preservation. Leaf removal is an important management technique in high altitude regions of Santa Catarina - Brazil, it improves wine chemical composition, and if carried out during the stages of full bloom, pepper corn berries and pea-sized berries can reduce the severity of Botrytis bunch rot; and avoid the formation of phenolic compounds related to the processes of oxidation and darkening.

Evaluation of leaf removal as a means to reduce nutrient concentrations and loads in urban stormwater

While the sources of nutrients to urban stormwater are many, the primary contributor is often organic detritus, especially in areas with dense overhead tree canopy. One way to remove organic detritus before it becomes entrained in runoff is to implement a city-wide leaf collection and street cleaning program. Improving our knowledge of the potential reduction of nutrients to stormwater through removal of leaves and other organic detritus on streets could help tailor more targeted municipal leaf collection programs. This study characterized an upper ideal limit in reductions of total and dissolved forms of phosphorus and nitrogen in stormwater through implementation of a municipal leaf collection and street cleaning program in Madison, WI, USA. Additional measures were taken to remove leaf litter from street surfaces prior to precipitation events.Loads of total and dissolved phosphorus were reduced by 84 and 83% (p<0.05), and total and dissolved nitrogen by 74 and 71% (p<0.05) with an active leaf removal program. Without leaf removal, 56% of the annual total phosphorus yield (winter excluded) was due to leaf litter in the fall compared to 16% with leaf removal. Despite significant reductions in load, total nitrogen showed only minor changes in fall yields without and with leaf removal at 19 and 16%, respectively. The majority of nutrient concentrations were in the dissolved fraction making source control through leaf removal one of the few treatment options available to environmental managers when reducing the amount of dissolved nutrients in stormwater runoff. Subsequently, the efficiency, frequency, and timing of leaf removal and street cleaning are the primary factors to consider when developing a leaf management program.

Effect of Early Fruit-Zone Leaf Removal on Canopy Development and Fruit Quality in Riesling and Sauvignon blanc

Canopy management is vital for quality winegrape production. During the 2012 and 2013 growing seasons, the timing of fruit-zone leaf removal (FZLR) was evaluated in two commercial vineyard blocks (<i>Vitis vinifera</i> Riesling and Sauvignon blanc) located north of Prosser, WA. Three different timings of manual FZLR were evaluated with a no-removal control. Leaf removal consisted of complete removal of all leaves and lateral shoots in the fruit zone on both sides of the canopy at prebloom, bloom, and four weeks postbloom. Each vine received the same treatment in both years. No negative implications were observed in total fruit set in either year. When leaf removal was performed, regardless of timing, the fruit zone of the canopy had less lateral shoot development and canopy refill than the control. Leaf removal also improved spray coverage in the fruit zone in Riesling, but the effect was related to the timing of leaf removal relative to the timing of the spray. In 2013, prebloom leaf removal significantly reduced Botrytis bunch rot severity in Sauvignon blanc (<i>p</i> = 0.01) below that of the control and four weeks postbloom leaf removal treatments. In 2013, prebloom leaf removal in Riesling increased terpene concentrations in the harvested juice (<i>p</i> = 0.03). In 2012, postbloom leaf removal in Riesling reduced concentrations of acids below those of the prebloom treatment (<i>p</i> = 0.04) in juice.

Pre-flowering leaf removal alters grape microbial population and offers good potential for a more sustainable and cost-effective management of a Pinot Noir vineyard

Background and Aims The grapevine canopy microclimate, particularly temperature and relative humidity, is of crucial importance for predisposing grapes to lower or greater incidence of microbial infections. Because of global warming, the widely adopted leaf removal at veraison causes an increase in the temperature of the grape berry surface, leading to sunburn and deterioration of berry composition. Seeking a good alternative, a novel, pre-flowering leaf removal was studied and compared with post-flowering approaches using a multidisciplinary approach. Methods and Results The effect of timing of leaf removal on the microbial ecology was studied in a Pinot Noir vineyard during two extremely different vintages. The effectiveness of leaf removal in suppressing Botrytis cinerea was compared with that of fungicide application. Bunch compactness and potential for cost and energy savings were calculated. The results showed that earlier leaf removal offers greater potential for successful control of microbial infections. Pre-flowering defoliation also led to lower bunch compactness (16–18%) accompanied by a substantial yield reduction (30% in 2010 and 24% in 2011). Conclusions In addition to improved microbial control, the lower yield from pre-flowering defoliation can eliminate the need for bunch thinning and consequently reduces total energy consumption; thus, the technique can be considered to have good potential for more sustainable and cost-effective management of the vineyard, saving 27% on costs and as much as 46% on energy. Significance of the Study The sustainability of a novel pre-flowering defoliation in Pinot Noir was evaluated by studying the microbial ecology of the vineyard and by calculating the potential savings from reduction in spraying and energy.

Use of Production Practices and Sensory Attributes to Characterize Loire Valley Red Wines

Quality wines are typically the product of soil, climate, and wine production practices. Sensory attributes are increasingly used to distinguish among Protected Designation of Origin (PDO) wines. Since 2010, the International Organization of Vine and Wine (OIV) is now taking all such parameters into account in the official ‘terroir’ definition. However, links between production practices and sensory attributes in geographically circumscribed PDO areas have not yet been investigated. This paper assesses production practices and sensory attributes of distinct PDO wines, within the same area. The study also identifies relationships between production practices and sensory attributes of these PDO wines. A survey was conducted to characterize production practices of thirty-three commercially produced PDO wines from the Loire Valley, France. Vineyard training systems, viticulture, harvest timing, winemaking and aging practices were studied. Descriptive sensory analysis was conducted to characterize the significant sensory attributes of these same wines. PDO wines were separated from one another by classical statistical analyses. About 25 percent of the analyzed production practices and less than fifty percent of the analyzed sensory attributes could differentiate PDO wines produced in the same area: respectively, percentage of Cabernet franc, time of leaf removal, harvest date, yield, duration of fermentation, duration of aging and use of oak, color intensity, viscosity, cloudiness, blackcurrant, prune, spicy, moldy, animal, bitterness and astringency. The study also identified links between some production practices and sensory attributes. The results of the study demonstrate that, under similar climatic conditions and soil characteristics, production practices and sensory attributes can distinguish PDO wines in well-defined geographic areas.

Phenolic composition of Tempranillo wines following early defoliation of the vines

Early defoliation is a viticultural practice aimed at crop control. So far, the impact of early leaf removal on the monomeric phenolic composition of wines has not been explored. This study examines the effects of early defoliation on the phenolic profile and content in Tempranillo wines. The influence of the defoliation method (manual vs mechanical) and the timing of leaf removal (pre-bloom vs fruit set) was investigated. Over two consecutive seasons, 2007 and 2008, the monomeric phenolic composition in Tempranillo wines was studied by high-performance liquid chromatography with photodiode array detection, and 22 compounds were identified and quantified. Overall, early defoliation led to wines more intensely coloured, of higher alcohol content and with larger concentrations of hydroxycinnamic acids, flavonols and anthocyanins (in 2008 only for mechanical treatments). In the absence of fungal infection, resveratrol was found to increase in wines corresponding to early defoliation treatments. The method of leaf removal seemed to be more critical than the timing of intervention, and larger effects on wine phenolic composition were observed for mechanical treatments. Early defoliation proved to be an effective technique for improving the phenolic composition of Tempranillo wines, by favouring the accumulation of hydroxycinnamics, flavonols and anthocyanins. This is an important achievement, as wine quality is often described by its colour and phenolic attributes.

Pinot Noir grape colour related phenolics as affected by leaf removal treatments in the Vipava Valley

Wine colour depends directly on the quantitative and qualitative profiles of anthocyanins, flavonols and hydroxycinnamic acids, as well as on their involvement in polymerization and co-pigmentation reactions. Pinot Noir is a grape variety with a low natural colour potential, often combined with problems of low colour stability for its wines during aging. The influence of leaf removal timing on grape colour related polyphenols was observed during maturation and at harvest time for the 2009 vintage “real scenario” conditions in two different vineyards in the Vipava Valley (Slovenia), known for its warm but windy climate. With different timing of leaf removal, a different microclimate can be achieved, with different light exposure for the specific plant tissue and different temperatures on berry surfaces. Phenolic compounds were characterised and quantified using HPLC/Vis. Three classes of polyphenols were affected by leaf removal timing, but with differing intensities and with some differences between locations. Hydroxycinnamic acids were affected only slightly, mostly at the beginning of the maturation period. Anthocyanins were significantly affected, while flavonols were the most affected by treatments in both vineyards and their concentration was clearly related to modification of the light within the canopy.

Effects of timing of leaf removal on yield, berry maturity, wine composition and sensory properties of cv. Grenache grown under non irrigated conditions

&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Aims&lt;/strong&gt;: The objective of this study was to investigate the effects of timing of leaf removal on yield components, berry sensory characteristics, composition and sensory properties of Vitis vinifera L. Grenache wines under non-irrigated conditions.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Methods and results&lt;/strong&gt;: The effects of timing of defoliation (fruit set and veraison) on yield components, berry maturity, wine composition and sensory properties of head trained, non irrigated, Grenache vines grown in Rioja appellation were studied. Leaf removal did not significantly modify total leaf area per vine as well as yield components. Grenache berries from early defoliated vines achieved the highest skin and technological maturity. Wine parameters, such as alcohol content, pH, titratable acidity, tartaric acid and total polyphenol index were unaffected by defoliation. Conversely, early leaf removal carried out at fruit set, significantly reduced the malic acid content of the wine and enhanced its colour intensity. Aroma complexity, mouthfeel, tannin quality and persistence were found to be significantly higher in the wine corresponding to the early leaf removal treatment. This was also the most preferred wine in terms of overall value.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Conclusion&lt;/strong&gt;: This article shows that timing of leaf removal had a marked effect on berry maturity, wine composition and sensory properties of Grenache wines made from grapes grown under dry-farmed conditions.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Significance and impact of study&lt;/strong&gt;: The results suggest that the timing of defoliation induces significant changes in Grenache wine composition and its sensory attributes. Late leaf removal was much less effective than early leaf removal in affecting final wine composition and quality. Grenache wine from the early defoliation treatment was rated the most preferred as of global value.&lt;/p&gt;

Frequency and Timing of Leaf Removal Affect Growth and Podophyllotoxin Content ofPodophyllum peltatumin Full Sun

Podophyllotoxin is a pharmaceutical compound found in leaves and rhizomes of American mayapple (P. peltatum L.), a species being investigated as an alternative to that of the Indian mayapple (P. emodi). Leaves alone can serve as a renewable source of podophyllotoxin (and other lignans) leaving rhizomes undisturbed to produce leaf biomass in subsequent years. It is not known, however, how frequently or severely plants can be defoliated without adversely affecting future plant growth, lignan content, or podophyllotoxin yield (g.m(-2)). This study compared harvest strategies that were mild to severe in frequency and timing of leaf removal. A wild population in full sun was subjected to leaf removal treatments of varying frequency (every year, every 2nd or 3rd year) and timing (early or late). Control plots not previously harvested were included every year. Plots were 1.0 m2 and established during spring of 2001. Duration of the study was four years. P. peltatum plants did not tolerate the most severe harvest treatment: annual harvest frequency in combination with early harvest time. Early annual harvests reduced total leaf dry mass and total leaf area in a consistent and linear manner. In contrast, plants tolerated annual harvests when conducted late in the growing season and tolerated early harvests when conducted every 2nd or 3rd year. The number of sexual shoots was reduced to zero by early annual harvests. Podophyllotoxin content was 2.7 to 6.5 times greater in leaves harvested early compared to those harvested late, though content was significantly greater in only two out of four years. In conclusion, we can recommend leaf removal every year from well-established P. peltatum populations grown in full sun if harvests are conducted late in the growing season. This harvest strategy ensures maximum podophyllotoxin yield without jeopardizing future leaf biomass yield. Leaves harvested early appear to have greater podophyllotoxin content, but we discourage early harvest every year. Instead, our results indicate that leaves can be harvested early every other year without reducing long-term performance of P. peltatum populations.

Frequency and Timing of Leaf Removal Affect Growth and Podophyllotoxin Content of American Mayapple in Shade

Leaves of American mayapple (Podophyllum peltatum) are being investigated as an alternative and renewable source of podophyllotoxin, a pharmaceutical compound used in the manufacture of several drugs. This study examined long-term performance of mayapple populations subjected to different harvest strategies. A naturally occurring population in shade was subjected to leaf removal treatments of frequency (every year, every 2nd or 3rd year) or timing (early or late season). Plots were 1.0 m2, established during Spring 2001, and treatments were applied from 2001 to 2004. Control plots not previously harvested were also included each year. Plants did not tolerate the severest of leaf removal treatments: early harvest time in combination with annual harvest frequency. Early annual harvests reduced total leaf dry mass and total leaf area in a quadratic manner. Late harvest conducted annually, and early harvest conducted every other year, also reduced leaf dry mass and area but not as much as early annual harvest. Plants harvested every year, early, or early every year produced fewer sexual shoots than other treatment combinations. Contents of α-peltatin, β-peltatin, and total lignans were higher for leaves harvested early than those harvested late during each year of the study, demonstrating that lignan contents were affected by leaf age and not treatment. In conclusion, our results for plants grown in shade show that leaves can be removed late in the growing season every 2nd or 3rd year or early every 3rd year without reducing long-term performance of the population. This is more restrictive than that reported for populations in full sun where plants tolerated late harvests every year.

EFFECTS OF LEAF REMOVAL ON YIELD AND FRUIT QUALITY OF `RIESLING' AND `CHARDONNAY' GRAPES.

Leaf removal has been reported to be beneficial to fruit quality of several grape cultivars. However, climatic conditions, time of leaf removal and genotype have a strong influence on the effect of leaf removal on fruit quality traits, such as soluble solids and titratable acidity. The effect of leaf removal on fruit quality of two vinifera grape cultivar grown in Minnesota was examined in this study. The first six basal leaves were removed from four canes on each vine of `Riesling' and `Chardonnay'. Leaf removal was carried out at two different times after the onset of verasion--early August (8/2) and late August (8/23). Fruit was harvested in late September and yield and fruit quality data were recorded. The results of the 1989 study will be discussed here. Leaf removal did not significantly affect yields obtained from either cultivar, regardless of leaf removal date. Early leaf removal on `Chardonnay' vines resulted in significantly higher soluble solids and significantly lower titratable acidity than that observed for fruit of control or late removal treated vines. Similar results were observed for `Riesling', however the differences were not significant. Data from 1989 and 1990 will he presented and discussed in the talk.

Effects of Timing and Severity of Leaf Removal on Yield and Fruit Composition of Sauvignon blanc Grapevines

Leaves were removed from mature, quadrilateral-cordon-trained Sauvignon blanc vines at fruit set, four weeks after fruit set, or seven weeks after fruit set. At each time, four levels of leaf removal were employed: Level 0 (control), no leaves removed; Level 1, basal leaves removed; Level 2, basal leaves plus leaves from top of canopy removed; and Level 3, basal leaves plus approximately three consecutive leaves at the top of the south-facing portion of the canopy removed to form a "window." The total soluble solids were significantly higher in fruit from vines with leaves removed. Titratable acidity, malic acid, pH, and juice potassium concentration were all significantly reduced by leaf removal. Increased severity of leaf removal further reduced the pH and potassium concentration in the berry juice at harvest. Yield, cluster number, cluster weight, and berry weight were not significantly affected by the level of leaf removal. Leaf removal significantly increased the photon fluence rate in the fruiting region of the canopy throughout the season. Significant negative correlations were obtained between the photon fluence rate and the pH, malate, and potassium concentration of the berry juice at harvest. A highly significant, positive correlation was found between the levels of malate and potassium in the juice at harvest. Timing of leaf removal did not significantly affect yield components or fruit composition, although earlier leaf removal tended to advance sugar accumulation.

THE EFFECTS OF LEAF REMOVAL ON YIELD AND YIELD COMPONENTS OF BRASSICA NAPUS

The effects of time of leaf removal on Brassica napus L. were studied under field conditions at Saskatoon in 1976 and at Swift Current in 1977. Leaf removal at the start of flowering reduced the number of pods per plant, increased seed weight, and reduced seed yield. Leaf removal at the end of flowering did not affect yield or its components.