WINETECH Technical Yearbook 2021

lower. The malic acid is unstable and drops out in the winemaking process, while the tartaric acid remains stable. • Bunches within dense canopies contain significantly lower levels of anthocya - nins (responsible for the red colour of the skins and wine) and phenols (which contain many flavour compounds). • Dense canopies also create ideal condi- tions for Botrytis rot and other diseases like downy mildew and oidium. Grapes stay damp for longer due to poor aera- tion and sprays cannot cover the grapes effectively. ALTERNATIVE SHOOT MANAGEMENT From the above-mentioned it should be clear that dense canopies should be avoided at all costs. Many producers resort to breaking out leaves to improve aeration of the canopy. This helps to an extent, but research has shown that sufficient sunlight exposure of developing vine buds are already required before flowering. The breaking out of leaves is done at the earliest after berry set (which is the best time) and in most cases only by pea berry stage. If suckering is not going to be performed, the better alternative is to pick up the foliage wires very early so that some of the shoots can sprawl, or to hook up the wires

before budding already and then leave for some shoots to grow through and others to sprawl (as can be seen in photo 2). This strategy can only work if the vines are not too vigorous. The shoots can easily collapse if vigour is too strong, a phenomenon which is also observed in bush vines. This in itself can lead to more densification. The approach towards tipping/topping should also be adjusted. Topping against the sides should be done cautiously to avoid short, infertile shoots (rugstekers). Shoots that sprawl to the sides, can be topped on the inside of the tractor row and should still contain 15 leaves, sufficient to ripen two bunches. PLANTING TO SPRAWL The search for a naturally more open canopy has led to new approaches with regard to the construction of trellis systems. To accommodate the more open canopies, row widths are being changed from 2.7 to 3 metres from the normal 2.2 to 2.5 metres. Tractor movement is eased by raising cordons from approximately 70 cm to 110 cm or more. A single or two fixed foliage wires are used to prevent shoots from collapsing and twisting around. Cultivars that have an upright growth habit, like Cabernet Sauvignon, Chardonnay,

PHOTO 1. The outer leaves of this canopy have been broken out to expose the dense interior. The yellow leaves are characteristic of a dense canopy.

PHOTO 2. The foliage wires were hooked up before budding to achieve a naturally more open canopy.

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