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.
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.
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.
With thanks to SAWIS for making the 2012 block data available.
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 firstname.lastname@example.org.
Hanno van Schalkwyk
VinPro viticultural consultant,
Paarl, Wellington & Swartland