Effects of trellising on water use, absorption of photosynthetically active radiation (PAR, 400 to 700 nm wavelength) by foliage and potentially by fruit, fruit composition, and yield were studied in 1988 under semi-arid conditions on field-grown Vitis vinifera L. 'Petite Sirah' grapevines in a mature vineyard. The positioning of shoots on trellises resulted in canopies that were (1) positioned vertically (vertical canopy), (2) positioned in a "V" pattern with sides inclined 60° from horizontal (inclined canopy), and (3) inclined toward the vineyard floor (standard canopy). Seasonal water use values determined from neutron scattering data were 393 ± 61, 554 ± 73, and 455 ± 57 mm for the standard, vertical and inclined canopies, respectively. On average, about 50% of seasonal water consumption occurred between fruit set and filling stages for each type of canopy. Average crop factors (ratio of actual to reference crop evapotranspiration) of 0.383, 0.540 and 0.444 were for the period bud burst to harvest for standard, vertical and inclined canopy systems, respectively. The diurnal water use patterns of the three trellising canopies were very similar when measured by either the heat pulse technique or by porometer. The average daily heat pulse velocity (HPV) for selected vertical, inclined and standard canopies for 6 days were 8.77, 7.58 and 6.85 cm h⁻¹, respectively. The HPV technique indicated that the average daily water use of the whole plant was 0.227, 0.192 and 0.137 kg/m² leaf area/d for standard, vertical and inclined canopies, respectively. The daily average transpiration rates as measured by the HPV technique were 32, 31, and 25% higher than the average transpiration rates estimated from porometer data for standard, vertical and inclined canopies, respectively. Stomatal conductances of the vertical and inclined canopies were 20 and 40%, respectively, below that of standard canopy. PAR absorption by foliage during mid-day was highest in the standard trellis, and lowest in the inclined trellis. PAR potentially available for absorption by fruits was lowest in the standard trellis, and highest in the inclined trellis. In both inclined and vertical canopies, the average sunfleck values were 26%, but was only 2% in the standard canopy. Analysis of fruit composition at harvest revealed that total dissolved solids (°Brix) was significantly higher in the inclined trellis than for the vertical trellis or the standard trellis. The inclined trellis resulted in the highest alcohol content of wine. Per vine yields did not differ significantly among the three trellis systems. Overall, the standard trellis was optimum because grapevines consumed less water and produced a shading which protected the fruit from direct solar radiation.

Modern canopy management practices and irrigation strategies have improved the economic and environmental sustainability of Australia ' s wine industry, in terms of increased production and improved wine quality for minimal production cost and environmental impact. This study tested the hypothesis that partial rootzone drying ( PRD ) integrated with low input, minimal pruning practices can improve sustainability of winegrape production in warm - climate, irrigated vineyards. The bi - factorial experiment investigated three conventional pruning practices; hand spur pruning ( SPUR ), mechanical hedging ( MECH ) and minimal pruning ( MIN ) integrated with standard drip ( SD ) and PRD irrigation strategies. The sustainability of winegrape production of field - grown cv. Shiraz grapevines was determined by examining yield, fruit composition, wine composition and quality, vine physiology and susceptibility of bunches to Botrytis bunch rot. Winegrape production was strongly influenced by pruning level and the resultant bunch number per vine. Increased node retention at pruning of minimal pruned vines resulted in 4 - fold more bunches per vine than spur pruned vines. Mechanical hedged vines had an intermediate number of bunches per vine. Yield generally reflected the trend in bunch number per vine. However, minimally pruned and mechanically hedged vines compensated for greater carbohydrate partitioning between reproductive sinks by producing smaller bunches with fewer berries per bunch. Partial drying of the grapevine rootzone had a detrimental effect on yield relative to SD irrigation ( 18 % ). The additive effect of SD combined with light pruning treatments resulted in few statistically significant interactions for the measured yield components. Berry weight was the only parameter influenced by the interaction between irrigation and pruning during the three experimental seasons ; PRD + MIN reduced berry weight by 36 % compared to SD + SPUR, in response to lower irrigation inputs and higher bunch number. A 2 - fold increase in water use efficiency ( tonnes per megalitre ) was found by the reduced irrigation inputs of PRD combined with the high crop levels of MIN vines compared to SD + SPUR vines. Fruit and wine composition was also largely unaffected by combined irrigation and pruning treatments, as a result of the additive effect of PRD and MIN. However, light pruning levels ( MIN and MECH ) and their associated small berry size and high bunch exposure, reduced pH and increased titratable acidity, and anthocyanin and phenolic concentrations of berry juice compared to SPUR. Minor pruning level effects on wine composition can be directly correlated with those observed on fruit composition. PRD had minimal effect on basic fruit composition but strong effects on wine spectral parameters : density, hue, total anthocyanin and phenolic concentration and ionised anthocyanin concentration, possibly as a result of co - pigmentation of anthocyanin compounds with exocarp tannins. Berry size was strongly correlated with fruit and wine quality. Small berries ( i.e. from PRD and MIN ) had lower pH and higher anthocyanin and phenolic concentrations in the juice and produced wine that was more acidic, brighter and had higher colour density and anthocyanin ( total and ionised ) and phenolic concentrations than all other treatments. Midday and diurnal leaf gas exchange were manipulated by partially drying the rootzone. PRD reduced midday stomatal conductance, photosynthesis and transpiration compared to SD. Stomatal limitation on photosynthesis and transpiration was probable, given the strong positive relationship with stomatal conductance and reduced carbon isotope discrimination by PRD. Transpiration efficiency was improved for PRD irrigated vines compared to SD irrigated vines. Leaf water potential and osmotic potential were measured diurnally, in conjunction with leaf gas exchange to investigate the response of PRD irrigated vines to increasing vapour pressure deficit. Diurnally, stomatal conductance was reduced by PRD compared to SD, which maintained leaf water potential, while no osmotic adjustment occurred. Therefore, PRD irrigation maintained hydraulic water status by hydrating half of the rootzone, whilst dehydration of the other half of the rootzone resulted in the partial closure of stomata. Pruning treatment effects on vine physiology were less pronounced. Minor gas exchange effects showed that pruning level influenced carboxylation efficiency and not stomatal limitations, as photosynthesis was not directly correlated with stomatal conductance. Bunches were least resistant to infection by Botrytis when fully developed and at maximum maturity. The development of bunches into tighter clusters as berry size increased from veraison to harvest and the increase in sugar content may have encouraged development of Botrytis. The distinct bunch architecture resulting from the combined pruning and irrigation treatments influenced the incidence and severity of Botrytis bunch rot. Light pruning combined with PRD irrigation produced small, loose bunches in season 2001 - 02, which were less susceptible to Botrytis bunch rot development compared to the large, compact bunches produced on SD + SPUR vines. However, low bunch numbers and high fruit - set on MIN and MECH vines in season 2002 - 03 led to a significant change in bunch architecture. As a consequence of the increased compactness of bunches in season 2002 - 03, no pruning effects on Botrytis development were observed. Long term economic and environmental sustainability of winegrape production is dependent on continual improvement in fruit and wine quality, preservation of yield, reduced water and chemical usage. This study has shown partial drying of the rootzone combined with light pruning techniques improved yield, fruit and wine composition, water use efficiency and transpiration efficiency and reduced the incidence and severity of Botrytis bunch rot compared to SD and severe pruning levels. Therefore, over the three experimental seasons, PRD combined with minimal pruning was determined as the preferred strategy to enhance the sustainability of winegrape production of Shiraz cv. in warm - climate, irrigated vineyards. / Thesis (Ph.D.)--School of Agriculture and Wine, 2004.

Several experiments were conducted to determine the influence of modifying the grapevine microclimate on the incidence of fruit rot and selected rot metabolites of Virginia grown White Riesling (<i>Vitis vinifera</i> L.) grapes. Due to the relatively high incidence of rot observed in these studies, an evaluation of the effects of rot on the sensory evaluation of juice and on selected aroma components was also undertaken. The effect of shoot topping to 10 or 20 nodes or the application of ethephon on the incidence of grape rot was measured for three seasons. Canopy modification by both topping and ethephon treatment increased sunlight penetration into the fruiting zone. Fruit rot incidence and the concentrations of rot-associated metabolites were significantly and mutually correlated. Fruit rots and rot metabolites were greatest with control and ethephon-treated vines and were least with vines whose shoots were topped to 10 nodes. In a separate three-year study, two to four leaves were removed from the fruiting zone of grapes grown on two training systems. Selective leaf removal generally increased sunlight penetration into the grapevine canopy. The incidence of Botrytis and sour rot as well as the concentrations of rot organism metabolites in harvested fruit were reduced by leaf removal. The effect of grape sour rot on general fruit chemistry, free volatile terpenes, potentially free volatile terpenes, selected polyols and rot metabolites was undertaken. Grape sour rot increased °Brix, glucose to fructose ratio, titratable acidity, tartaric acid, glycerol and gluconic acid. Grape sour rot reduced the concentrations of geraniol, nerol and linalool, while increasing oxidation products, aromatic alcohols and long chained alcohols. Grape juice sensory analysis appeared to be influenced by the severe fruit rot which occurred in both the control and to a lesser extent in canopy manipulated vines in both studies. The importance of fruit rot was demonstrated by both the production of odors, metabolites, and the destruction of native grape aroma constituents. Reductions in the incidence of fruit rot by selective leaf removal and shoot topping were demonstrated and were probably due to several microclimate factors that collectively increased evaporative potential and spray penetration into the fruit zone. The results illustrate that remedial canopy management practices that improve fruit zone porosity can mitigate the severe disease pressure that exists when rot-prone cultivars are grown in humid grape growing regions. The inability to reduce fruit rots further than noted in these studies may be due to the complex nature of fruit rots observed here, compared to those (principally Botrytis rot) examined in the majority of other canopy management studies. / Master of Science

Thesis (MScAgric)--Stellenbosch University, 1946. / No Abstract Available

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The financial decision-making environment within which wine-grape producers function is challenging because of the complex interrelationships between yield, product price and input requirements. The complexity of farm systems is increased because production and financial decisions are necessarily made under uncertainty. Various issues influence the resilience of the wine industry. The goal of this study is to determine the financial implications of irrigation, integrated with canopy management practices on red wine cultivars in the Robertson area. Canopy management and irrigation cost play an important role within the multi-faceted farm system regarding yield, quality and input cost. This necessitates that research be carried out within the context of a systems approach. In this manner the interdependence among the various components of the farm system, and the associated synergies can be captured. Farm management, as a field of research, is dependent on other disciplines that present an alternative perspective to the research problem. Viticulture trials specifically focused on the impact of various irrigation and canopy management activities is being done on Wansbek farm. Nine treatments were tested at various combinations of soil water depletion levels and canopy management strategies. The farm is situated in Agterkliphoogte, an area in the Robertson valley. A multi-disciplinary group discussion was held to firstly obtain insight in the complex working of a farm. Secondly the group discussion was used to gain insight into the application of the Wansbek trial data and the setting of guidelines as to its application to determine the expected farm level financial implications of the treatments. Dealing with complexity necessitates insight form various areas of expertise, which is achieved time efficiently within expert group discussions. A quantitative method is required to reflect the interrelatedness and dynamics of a whole farm system in a user-friendly manner. Multi-period budget models present the ability to accommodate the complexity associated with a farm through a sequence of mathematical and accounting equations. The physical/biological interrelations and structure of the farm can be modelled while the financial performance of various irrigation and canopy management strategies can be determined. Farm-level profitability is especially sensitive to yield and price of farm products. The treatments that showed the highest expected profitability, return relatively high yields and prices at relatively low production costs. The sprawling canopy management treatment at c. 60% and c. 30% plant available water depletion levels returned the highest and second highest profitability at both gross margin per hectare and whole farm level. Scenarios were incorporated to illustrate the expected impact of key variables and the capability of the model. Key factors associated with the success of specific treatments could be identified. Results showed throughout that the balance between yield, price and input cost are the determining factor to profitability, rather than a focus on any particular one of these factors. / AFRIKAANSE OPSOMMING: Die finansiële besluitnemingsomgewing waarbinne wyndruifprodusente funksioneer, is uitdagend weens die komplekse verwantskappe tussen oesopbrengs en -kwaliteit en gepaardgaande insetbehoeftes. Die kompleksiteit van die boerderystelsels word verhoog deurdat produksie- en finansiële besluite noodwendig op grond van onvolmaakte inligting geneem word. Verskeie kwessies beïnvloed die voortbestaan van die wynbedryf. Die doel van hierdie studie is om die finansiële implikasies te bepaal van besproeiing, geïntegreer met lowerbestuur, vir rooi wyndruifverbouing in die Robertson-wynvallei. Lowerbestuur- en besproeiingkoste speel ʼn belangrike rol binne die multifasettigheid van ʼn boerderystelsel ten opsigte van opbrengs, kwaliteit en produksiekoste. Dit vereis dat die navorsing binne die konteks van die stelselsbenadering aangespreek word. Sodoende word die interafhanklikheid tussen die onderskeie boerderystelselkomponente, gekoppel aan die sinergistiese effek wat daarmee gepaardgaan, in ag geneem. Boerderybestuur as navorsingsveld, is gevolglik afhanklik van ander vakdissiplines wat ‘n alternatiewe perspektief verleen aan die navorsingsprobleem. Wingerdbouproewe wat spesifiek fokus op die impak van verskillende besproeiing- en lowerbestuursaksies word uitgevoer op die Wansbek-plaas. Die plaas is geleë te Agterkliphoogte, ʼn area in die Robertson-vallei. Nege behandelings is getoets teen verskillende kombinasies van plant beskikbare water (PBW)-onttrekkingspeile en lowerbestuurstrategieë. ʼn Groepsbespreking met multidissiplinêre deskundiges is gehou om eerstens, insig in die kompleksiteit van die werking van ʼn plaas te verkry. Tweedens, is die groep van multidissiplinêre deskundiges gebruik om insig te verwerf aangaande die hantering van die Wansbek-proefdata. Die groep het riglyne daargestel om die proefdata prakties aan te wend sodat die verwagte finansiële implikasies op plaasvlak geëvalueer kan word. Die hantering van kompleksiteit vereis insig vanuit verskeie gebiede van kundigheid wat tydsdoeltreffend binne ʼn groepsbespreking van multidissiplinêre deskundiges geakkommodeer kan word. ʼn Kwantitatiewe tegniek is nodig om die wisselwerking en dinamika van ʼn geheelboerderystelsel op ʼn gebruikersvriendelike en toepaslike manier te weerspieël. Multiperiode-begrotingsmodelle gee die vermoë om die kompleksiteit, wat met ʼn tipiese plaas geassosieer word, te akkommodeer deur die toepassing van basiese wiskundige en rekeningkundige beginsels. Die fisies-biologiese wisselwerking en struktuur van die plaas kan sodoende gemodelleer word, terwyl die finansiële prestasie van die kombinasies van verskillende besproeiing- en lowerbestuurstrategieë bepaal kan word. Die plaasvlakwinsgewendheid is veral sensitief vir die opbrengs en prys van produkte gelewer. Die behandelings wat die beste verwagte winsgewendheid getoon het, produseer teen ʼn relatiewe hoë produksie en prys en ’n relatiewe lae produksiekoste. Die oophanglowerbestuurbehandeling teen c. 60% en c. 30% plant beskikbare water-onttrekkingspeile is die mees en tweede mees winsgewende strategieë op per hektaar bruto marge en geheelplaasvlak. Die gebruik van scenario’s is geïnkorporeer om die impak van sleutelveranderlikes uit te wys en die vermoë van die model te illustreer. Sleutelfaktore tot die sukses wat aan sekere strategieë verbind word, kan sodoende uitgewys word. Deurgaans wys die resultate dat die balans tussen opbrengs, prys en produksiekoste belangriker is as die fokus op enige enkele een van die faktore.

Thesis (MscAgric (Viticulture and Oenology))--University of Stellenbosch, 2006. / Under certain South African conditions, Redglobe develops a colour that is too dark and thus unacceptable for the Far Eastern markets. These markets require a pink colour instead of a dark red colour. The cultivation of grapes with an acceptable colour involves amongst other, canopy management practices. This generally includes the removal of leaves and/or lateral shoots. Hereby, the leaf area and the microclimatic conditions in the canopy are altered. The aim of this study was to test the usefulness of leaf and lateral shoot removal at different defoliation times after anthesis in order to obtain a pink coloured Redglobe crop. Other quality aspects, namely total soluble solids (TSS), total titratable acidity (TTA), berry mass and total yield, were also evaluated. A canopy management trial was conducted on six year old Redglobe vines with moderate vigour. The treatment design was a 2 x 3 x 4 factorial and involved two leaf removal (L) levels (L0 = 0% leaf removal; L33 = 33% leaf removal) in combination with three lateral shoot removal (LS) levels (LS0 = 0 % lateral shoot removal; LS50 = 50% lateral shoot removal; LS100 = 100% lateral shoot removal). Four defoliation times (DT) were selected: 36 (pea berry size), 69 (véraison), 76 (one week after véraison) and 83 (two weeks after véraison) days after anthesis (DAA). A total of 24 treatment combinations, replicated in four blocks, were applied. Generally, treatment combinations involving 33% leaf removal lowered the main shoot leaf area. Likewise, the lateral shoot leaf area was decreased by increasing levels of lateral shoot removal at any defoliation time. As expected, 33% leaf removal applied in combination with any level of lateral shoot removal, always resulted in a lower total vine leaf area compared to where 0% leaf removal was part of the treatment combination. Compensation reactions occurred and in this regard the main shoot leaf size increased due to 33% leaf removal applied at 1 week after véraison and 2 weeks after véraison. Treatment combinations involving lateral shoot removal increased the ratio of main shoot leaf area to the total leaf area. On the other hand, the main shoot leaf area percentage was lowered by the application of 33% leaf removal at 2 weeks after véraison compared to no leaf removal at the same defoliation time. It can therefore be assumed that the contribution of lateral shoot leaves to grape composition might have increased in cases where the main shoot leaf area was lowered at a later stage (e.g. 2 weeks after véraison). The bunches were visually evaluated and divided into classes from dark (class one) to light (class nine). This visual bunch evaluation showed that the mean bunch colour was in class three (lighter than class two) due to the defoliation time. The lateral shoot removal x leaf removal interaction resulted in a mean bunch colour that was in classes 2 and 3. However, within these classes, there was a tendency that bunch colour decreased for defoliation times later than pea berry size. The lateral shoot removal x leaf removal interactions showed that bunch colour was darker when the treatment combinations involved 0% leaf removal. The percentage of bunches with the desired colour was increased by application of the treatments at véraison, compared to the other defoliation times, and also with 50% lateral shoot removal and 100% lateral shoot removal compared to 0% lateral shoot removal. Biochemical analyses confirmed that increased levels of lateral shoot removal generally lowered the anthocyanin concentration regardless of defoliation time. A similar effect on TSS was observed, i.e. from véraison onwards, the application of 50% lateral shoot removal and 100% lateral shoot removal tended to lower TSS. The effect of these levels of lateral shoot removal at véraison was significant. The role of the lateral shoots in colour development and sugar accumulation is therefore emphasized. Furthermore, the special role that lateral shoots also play in berry development is illustrated in that berry mass tended to decrease when 100% lateral shoot removal in combination with 33% leaf removal and 100% lateral shoot removal in combination with 0% leaf removal were applied at véraison. This, together with the positive relationship obtained between grape colour and the lateral shoot leaf area:fruit mass ratio, accentuates the role of active leaf area during the ripening period. The possible effect of the microclimatic light environment on colour must also be considered. However, although the light intensity increased with increased levels of LS, the colour that was obtained was probably not associated with the differences in light intensity. It was found that it is possible to manipulate the colour of Redglobe grapes with defoliation treatments. However, the treatments that have a decreasing effect on grape colour also affected other quality parameters like TSS and berry size negatively. Although, it is possible to reduce the colour of Redglobe through the application of leaf and lateral shoot removal at different defoliation times, the question arises whether the treatment combinations used in this study are worthwhile to pursue because the mean bunch colour that was obtained was still too dark. However, it was possible to increase the percentage of bunches with the desired colour. Therefore, if such treatments are applied, it must be approached cautiously, keeping in mind that assimilate supply has to be sustained throughout the ripening period.