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Cultivation of Pinotage in various climatic regions (Part 1):
Climatic differences
Danie van Schalkwyk & André Schmidt, ARC Infruitec-Nietvoorbij, Stellenbosch
Key words: Climate, cordon height, canopy management, Pinotage, vine development, wine quality.
INTRODUCTION
Pinotage first appeared in 1925 and is currently South Africa’s most important locally developed red wine cultivar. Within a relatively short period Pinotage wines have achieved recognition among top end wines on local as well as foreign markets. Pinotage has a unique character and the wines mature very well. Although one finds increasingly fewer inferior wines, it is unfortunately true that inferior wines are still being made. Poor wine quality is not inherent to the cultivar, instead it possibly results from incorrect application of viticultural and vinification techniques. Pinotage is precious to South African winemakers and the Pinotage Association was founded in 1995 with the purpose of improving the quality of Pinotage wines and promoting the marketing of top quality Pinotage throughout the world. Pinotage performs extremely well at domestic and foreign wine shows, such as the Veritas Awards, where it has received hundreds of awards since 1991, , hence the increased demand for Pinotage wines on foreign markets.
BELOW FIGURE 1. Average February temperature (AFT) of Pinotage cultivation areas.
BELOW FIGURE 2. Different vine frames used in the Pinotage project. (click image to enlarge)
According to 1996 SAWIS statistics, approximately 380 ha Pinotage were planted in 1995, making it the most popular red wine cultivar for new plantings at that stage (Anon, 1996). At one stage the demand for Pinotage vines was so great that there was a shortage of certified material in the 1996 and 1997 seasons. Pinotage currently constitutes 6.4% (6 493 ha) of all wine grape plantings and is the fourth most planted red wine cultivar in South Africa (Anon, 2006).
Table 1 (click image to enlarge)
Table 2 (click image to enlarge)
Viticulturally Pinotage is very well adapted to Western Cape cultivation conditions and no serious cultivation problems are known. It is grown successfully in practically all the climatic regions, from the cooler conditions (average February temperature 19°C - 21°C) to the warmer conditions (average February temperature 22°C - 23°C). Depending on the virus status of the material, grapes ripen from the end of January to mid-March in the Western Cape.
Pinotage grows with moderate vigour and has a fairly upright bearing. In the past it was mostly developed as bush vines and only later trellised on vertical trellis systems. The cultivar fares extremely well under dryland conditions, under which it is mainly cultivated as bush vines. There is a perception among winemakers that higher quality Pinotage wines generally derive from older bush vine plantings, and consequently that bush vine and premium wines are synonymous, hence the trend to recommend bush vine development. This advice is also endorsed by the Pinotage Producers’ Association. This contention has not been scientifically proven.
The better wine quality from old bush vine vineyards can possibly be ascribed to the different characteristics of the canopy that occurs among young, vigorous, mostly dense, trellised vines that have been established with improved plant material compared to the less vigorous old bush vines. Older bush vines usually have open canopies and the grapes are quite exposed to direct sun. It has also been found that temperatures in the canopy decrease with an increase in height above the surface of the soil (Strauss & Archer, 1986). Grapes from the older bush vines therefore ripen in warmer and more exposed climatic conditions. Research at Nietvoorbij has shown that the development of flavourants, depending on the cultivar, can be improved or compromised by direct exposure to sunlight and temperature (Marais, 2005). It has been proven scientifically that the development of the vine has a significant influence on the phenolic composition of grape skins (Tambora et al., 2003). The influence it has on flavour development in Pinotage remains fairly unknown.
There is consequently a fair amount of uncertainty about whether bush vines or trellised vines produce the best quality Pinotage wines and whether the cultivar should be grown under cooler or warmer conditions to produce unique wines of exceptionally high quality. In an attempt to find answers to these questions, ARC Infruitec-Nietvoorbij launched a project in 1998 with financial support from Winetech and the Pinotage Association to investigate the influence of vine development (trunk height and cordon orientation) and canopy density (exposure of grapes) on the wine quality of Pinotage in climatic regions 2, 3 and 4 in the Western Cape.
TRIAL PROCEDURE
The extent and cost of a properly laid out field trial in each of the three climatic regions would be extremely high, consequently seven trial sites were laid out in existing young (1 to 2 years) Pinotage vineyards at various producers in each of climatic regions 2, 3 and 4 for statistical purposes (Le Roux, 1974; Winkler et al., 1974). Each producer site was considered a repetition and the treatments were applied in a randomised fashion. These sites were selected based on macro-climatic data according to Average February Temperature (AFT) (De Villiers, et al., 1996) with climatic region 2 (19°C - 21°C), climatic region 3 (21°C - 23°C) and climatic region 4 (23°C - 25°C) (Fig. 1). The trial sites were spread throughout the Western Cape with sites in Darling, Riebeek-West, Wellington, Agter-Paarl, Perdeberg, Kuils River, Stellenbosch, Somerset West and Hermanus vicinity (Table 1).
Pinotage vines from the same clone (PI 48) were used and developed according to four vine development methods, i.e. bush vine with 20 cm trunk length, bush vine with 30 cm trunk length, split cordon with 30 cm trunk length on Extended Perold (EP) and split cordon with 60 cm trunk length on an Extended Perold (Fig. 2). Both split cordon treatments had moveable foliage wires. The normal recommended vine development (green shoot in the case of split cordon), bearer spacing [12.5 cm (8 two bud bearers per running metre cordon) between bearers for split cordon and 5 - 6 two bud bearers in cup format for bush vine] were applied and suckering practices following during vine development. Crop control was applied through bunch removal in the vine development stage.
Two canopy management treatments were applied randomly from 2002 onwards. With the minimal canopy management (MC), suckering took place between the bearers only and all the shoots budding on the bearers were left in place and no leaves were removed. With optimal canopy management (OC), suckering took place between the bearers and only two shoots were left per bearer. Leaves were also removed where necessary according to the norms recommended by Hunter (1992) (Photo 1 & 2). If the building up of bearers occurred due to poor budding, a renewal shoot was left in place in the latter treatment.
FIGURE 3. Average monthly temperatures above 30, 35 and 40°C in climatic regions 2, 3 and 4 (2003 - 2007).
Canopy density was determined by means of the point quadrant method during veraison (Hunter, 1992). Each treatment’s canopy was also evaluated using an evaluation chart during the harvest to determine the effectiveness of the application of optimal canopy management as opposed to the minimal canopy management (Hunter, 1999). Light intensity was determined inside and outside the canopy during 2006 and 2007 to quantify the photosynthetic active radiations (400 - 700 nm) inside the various canopies.
During 2004 temperature loggers were installed at the trial sites approximately 1 m above the surface within the canopy of the 60 cm trellised treatments in order to monitor the average temperatures over every five minutes inside the canopy during ripening (Photo 3 & 4).
Grapes from each treatment were harvested at a ripeness of 24°B - 25°B and experimental wines were made from 2003 onwards in Nietvoorbij’s experimental cellar according to the experimental method for red wines. Each season’s wine quality and maturation potential was judged according to standard sensorial procedures by a trained judging panel using the 10-point line scale method 6 and 24 months after bottling. Wines were evaluated for the main aromas only, i.e. cherry, berry and plum aromas (the data are discussed in subsequent articles).
Grapes and wine from this experiment were also supplied to other researchers for different Pinotage projects and some of the results are mentioned in this series of articles.
RESULTS AND DISCUSSION
The average number of hours per month when the temperature exceeded 30°C, 35°C and 40°C, were calculated to quantify heat periods (Fig. 3). These figures reflect just how warm it actually was in the various regions and also indicate the length of the period when hardly any photosynthetic activity took place. This type of calculation is a better norm than the average maximum temperature per day as it indicates the truly exceptionally warm periods.
The number of hours above 30°C for the corresponding period from 16 December to the end of February for the 2003/2004 to 2006/2007 seasons are compared in Table 2. When comparing the total number of hours above 30°C within the various climatic regions over seasons, it is clear that during 2003/2004 climatic region 2 was much warmer than climatic region 3. This was also confirmed by the average temperatures for the corresponding periods. The occurrence is mainly ascribed to the two heatwaves during January and February 2004 when the temperatures exceeded 30°C for long periods and even exceeded 40°C in climatic region 2. Although this is not reflected by the average temperatures, the 2005/2006 season was generally warmer than the previous two as well as the 2006/2007 seasons, when taking into account the number of hours above 30°C. During 2005/2006 high temperatures lasted for longer periods per day. Despite the heatwave from 21 to 25 January 2007, the 2006/2007 ripening period was the coolest over the past four seasons.
During the 2005/2006 season there were periods when maximum temperatures inside the canopies in climatic region 4 were above 30°C for up to 12 hours per day and on two occasions above 35°C for 6 hours per day for 6 consecutive days. Consequently long periods occurred when hardly any photosynthetic activities occurred. In February 2005 climatic region 4 had an average of 10 hours above 40°C. Temperature data above 30°C indicate that the 2005/2006 season, in climatic region 4 especially, was considerably warmer than the two previous seasons and the 2006/2007 season. It is obvious that a calculation of the average daily temperatures can be misleading and does not really indicate how long the warm weather lasted.
Heatwaves have a major effect on grape quality, but the effect of long warm periods during the day should not be underestimated and these probably have a bigger influence on grape and must quality and eventually on wine quality. Heatwaves during ripening resulted in a huge loss of foliage at some of the trial sites, especially in climatic region 2. Temperatures of up to 46°C were measured in some of the canopies in January 2007. Because of heatwaves 50% of the bunches of the 30 cm and 60 cm trellised treatments on one of the farms in climatic regions 2 had to be removed annually to prevent the vines from being subjected to excessive stress. Macro-weather station data indicated that more wind occurred during the 2005/2006 season in climatic region 4 which could have dried out the soil considerably (data not shown). In 2005 the drier conditions caused brackish conditions in one of the sites in climatic region 4, in bands throughout the entire vineyard block, causing some of the vines to lose all their leaves (Photo 5).
When the average temperatures and harvest dates of Pinotage in the different regions are taken into account, it seems that average January temperatures are a better norm for the cultivation of Pinotage than average February temperatures.
CONCLUSIONS AND RECOMMENDATIONS
It is important to monitor temperatures inside the Pinotage canopy because this indicates the length of the period when temperatures exceed 35°C during heatwaves and hardly any photosynthetic activity is able to take place. Average maximum temperatures obtained from macro-weather stations can be misleading as they do not give any indication of the actual length of the hot periods. Lengthy warm periods during heatwaves can impact negatively on the grape quality, must and eventual wine quality of Pinotage.
Another factor that emerged from this investigation is that January temperatures are probably a more accurate norm for the division of Pinotage cultivation areas into climatic regions, seeing that most Pinotage sites, especially in climatic region 4, had finished harvesting at the beginning of February.
ACKNOWLEDGEMENT
Financial support by Winetech, Pinotage Association and ARC.
For more information contact Danie van Schalkwyk at ARC Infruitec-Nietvoorbij, e-mail; vschalkwykd@arc.agric.za.
REFERENCES
Anon, 1996. SA Wynbedryfstatistiek nr. 20. KWV, PO Box 528, 7624 Suider-Paarl.
Anon, 2006. SA Wynbedryfstatistiek nr. 30. SAWIS, PO Box 238, 7620 Paarl.
De Villiers, F.S., Schmidt, A., Theron, J.C.D. & Taljaard, R., 1996. Onderverdeling van die Wes-Kaapse wynbougebiede volgens bestaande klimaatskriteria. Wynboer Tegnies 78, 10 - 12.
Hunter, J.J., 1992. Manipulering van lower vir optimum gehalte druiwe. Winegrape Summer Workshop, p. 1 - 22. 3 December 1992, Stellenbosch.
Nietvoorbij Institute for Viticulture and Oenology.
Hunter J.J., 1999. Present status and prospects of winegrape viticulture in South Africa. Proc. 11th Meeting study group for vine training systems. June 1999, Marsala, Sicily, Italy. 70 - 85.
Le Roux, E.G., 1974. ’n Klimaatsindeling vir die Suidwes-Kaaplandse wynbougebiede. M.Sc. thesis, Stellenbosch University, 7600 Stellenbosch.
Marais, J., 2005. Effect of berry size, sunlight exposure and ripeness on Chenin blanc quality. Wynboer Technical Yearbook 2005/6, 88 - 90.
Tamborra, P., Este, M., Minafra, M. & Sinesio, F., 2003. Phenolic compounds in red-skins of Uva di Troia and Bombino nero grapes (Vitis vinifera L.). Ital. J. Food Sci. 15, 347 - 357.
Strauss, H.C & Archer, E., 1986. Oplei van wingerd. l. Agtergrond en beginsels. Boerdery in Suid-Afrika, NIWW 177/1986.
Winkler, A.J., Cook, J.A., Kliewer, W.M. & Lider, L.A., 1974. General Viticulture. Univ. Calif. Press, Berkley.
ABSTRACT
Temperatures monitored in the canopies of the 60 cm trellis treatments indicated that long periods of extreme temperatures above 35°C occurred during January and February. Up to 12 hours above 30°C per day were registered and during one year temperatures were above 35°C for 6 hours/day for 6 consecutive days, indicating that long periods occurred during ripening during which no photosynthesis occurred. Maximum temperatures obtained from macro-weather stations are deceptive as they usually do not give an indication of the period of excessive hot periods. These hot conditions resulted in excessive loss of leaves at some of the plots and sun burn of the exposed grapes. During these long hot periods, grapes of the minimal canopy management treatments were less subjected to sunburn as more leaves were present to protect bunches. As Pinotage reached optimal ripeness and grapes were harvested between the second week in January and the second week in February, the mean January temperatures rather than those of February should be used to classify Pinotage cultivation areas into different climate regions.
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