Introduction
The use of bush vines has long been declining in the Stellenbosch, Malmesbury and Paarl regions, according to Archer (1991).In the Stellenbosch area the percentage grapevines being cultivated as bush vines decreased from 59% in 1971, to 38% in 1979 and 30% in 1987. According to the 2012 SAWIS block data, 23% (excluding one-year-old blocks) of the surface planted to grapevines in Stellenbosch was cultivated as bush vines.It is estimated that 80 to 90% of wine grapes in the Malmesbury (Swartland) district were being cultivated as bush vines in the late 1980s (Archer, 1991). The latest SAWIS block data show that 47% of grapevines in this area are not trellised.

One of the reasons for the move away from bush vines is probably the objective of higher productions which is enabled by trellis systems, in conjunction with the greater availability of irrigation water. Furthermore, the focus on mechanisation is ever increasing and the fact that pruning and harvesting processes on bush vines cannot be mechanised, impacts on producers’ considerations at the time of establishment.

Current status
The 2012 SAWIS block data were used to investigate the current status of bush vines. Year-old plantings were ignored, seeing that the majority of these blocks are trellised in their second year.

Approximately 15% of the total surface planted to grapevines was cultivated as bush vines. As far as the regions are concerned, 91% of bush vine plantings were situated in Malmesbury (6 404 ha; 47% of regional surface), Stellenbosch (3 722 ha; 23% of regional surface) and Paarl (3 449 ha; 22% of regional surface). According to the block data, 54% of the total bush vine status was cultivated as dryland vines. Bush vines are especially suitable when the anticipated vigour is low; under these circumstances the additional cost of trellising is often not justified. Such terrains are simply not able to realise higher productions.

No fewer than 67 cultivars are cultivated as bush vines and Figure 1 shows the surface represented by the most important cultivars.

Cultivars with a naturally upright growth pattern are easier to shape and cultivate as bush vines. Experience shows that cultivars such as Shiraz, which have more supple shoots, require more input for successful cultivation as bush vines.

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PHOTO 1. A temporary support pole is used to shape the cup of this Grenache noir bush vine away from the soil surface.

FIGURE 2. The most important cultivars (according to hectares planted) that were cultivated as bush vines in the Malmesbury, Paarl and Stellenbosch areas in 2011.
FIGURE 1. The most important cultivars (in terms of hectares) cultivated as bush vines in South Africa in 2011 (SAWIS 2012 block data).
PHOTO 3. High density bush vine Chenin blanc plantings near Riebeek-West.
PHOTO 2. Old poles and a single wire were used to form the cup of this Cinsaut bush vine about 40 cm above the soil surface.
TABLE 1. A comparison of the age distribution of bush vines and trellised vines (total surface planted to grapevines) in 2011.

 

Within the regions, the cultivar composition differs as can be expected, the outliers being Chardonnay, Cabernet franc, Merlot and Sauvignon blanc in Stellenbosch, and Cinsaut in Paarl, with relatively bigger plantings than in the other regions.

As expected Table 1 indicates that the trellised grapevine segment in general comprises more younger grapevines (less than 10 years), with producers trellising their grapevines to a greater extent. In recent years more plantings have also been taking place in the irrigation areas, where trellising of grapevines is the norm.

Among the 10% of bush vines older than 30 years, several blocks have been identified that are producing exceptional terroir wines. Old bush vine Chenin blanc in particular has achieved prominence in recent years and excellent examples of these complex and unique wines keep emerging. At average prices, however, these old vineyards are not sustainable.

Microclimate and irrigation requirements
During a trellis trial in Robertson, Van Zyl and Van Huyssteen (1980) found that temperatures within the canopy, as well as bunch temperatures, were higher in the case of bush vines compared to Perold and extended Perold systems. From véraison to harvest the bunch temperatures in the bush vines at 12:00 were on average 6.73°C higher than in the case of the extended Perold. It was found that bushvine bunches were more exposed to the sun and that bunches also received more reflected heat from the soil surface. This can be a big advantage in cool areas where late cultivars struggle to ripen. In warm areas, however, higher bunch temperatures during ripening are unwanted, and producers are making various plans to get the grapes away from the soil more quickly (Photos 1 & 2).

Due to higher ambient temperatures inside the bush vines, increased aeration and less shadowing of the soil surface, the evapotranspiration tempo of the bush vines was much higher than that of trellised grapevines (Van Zyl & Van Huyssteen, 1980). Under irrigation conditions in Robertson, the irrigation requirements for bush vines, a Perold system, an extended Perold system and a slanted roof, from bud burst to post-harvest, were calculated at 404.1 mm, 294.1 mm, 339.2 mm and 351.3 mm respectively. Under such conditions the bush vines, with less than half the production of the other systems and greater irrigation requirements, produced poor results.

High density
Producers in the Swartland who have a very good market for specific bush vine Chenin blanc, but still have to make every effort to achieve high unit productions, are planting at high density with productions of 20 tons/ha and higher being achieved (Photo 3). In such instances irrigation water is available and each row has been provided with a drip line.

Summary
The cultivation of wine grapes as bush vines has decreased and is expected to decrease even further as a result of increasing pressure to mechanise. Producers should also aim to achieve high unit production, which is only possible by means of bigger trellis systems (leaf surface).

Bush vines nevertheless remain an option on lower yield terrain (for example dryland with sufficient soil moisture content), where an expensive trellis system does not necessarily ensure higher productions. Often such terrain allows for balanced grapevines with moderate growth and yield, from which concentrated and high quality wines can be made. The challenge is therefore to find value for such wines in the markets. Only then will the iconic bush vine be able to remain a sustainable part of our vineyard landscape.

Acknowledgement
With thanks to SAWIS for making the 2012 block data available.

References
Archer, E., 1991. Oplei van wingerdstokke. Department of Viticulture and Oenology, Stellenbosch University.
Van Zyl, J.L. & Van Huyssteen, L., 1980. Comparative studies on different trellising systems (I): Consumptive water use. South African Journal of Enology and Viticulture 1: 7 – 14.
Van Zyl, J.L. & Van Huyssteen, L., 1980. Comparative studies on different trellising systems (II): Micro-climatic studies, grape composition and wine quality. South African Journal of Enology and Viticulture 1: 15 – 25.

For further information contact Hanno van Schalkwyk at hanno@vinpro.co.za.
Hanno van Schalkwyk
VinPro viticultural consultant,
Paarl, Wellington & Swartland

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