WINETECH Technical Yearbook 2021

PRACTICAL IN THE VINEYARD | AUGUST 2021

Is shoot positioning always a good thing?

DISADVANTAGES OF DENSE CANOPIES

• The leaves within a dense canopy cannot utilise potassium optimally, and excess potassium is ultimately deposited into the grapes. This in turn leads to salt formation with organic acids and a subsequent increase in the pH levels of the wine. High pH levels in wine weaken the activity of sulphur dioxide in that less of it occurs in free, active form leaving the wine susceptible to microbiological instability. • A perception exists that dense canopies give higher titrable acid levels, which indeed is the case. Further analyses reveal however, that the malic acid levels are higher and the tartaric acid

It has already been proven that dense vineyard canopies are extremely detrimental for crop size as well as wine quality. The following are some of the negative consequences: • Sufficient sunlight exposure on the developing vine buds is needed for good fertility. The vine buds that develop during the spring, already contain the beginnings of the crop (flower cluster primordia) that will be harvested in 15 months. Dense canopies will over time yield fewer and smaller bunches.

HANNO VAN SCHALKWYK: Vinpro, Paarl KEYWORDS: Shoot positioning, vineyard management.

four to seven fixed foliage wires through which shoots are weaved.

THE PURPOSE OF SHOOT POSITIONING, mostly with the help of moveable foliage wires, is to position shoots upright and expose leaves to the maximum amount of sunlight. In this regard it can almost be compared to a solar panel. Wine producers have in recent years been under great financial pressure and therefore costs are being cut in order to survive. In practice, especially in the case of bulk and entry-level wine blocks, suckering actions have been abandoned or significantly downscaled. The question is whether we can continue to position shoots as before? As can be seen from figure 1, approximately 40% of vineyards in South Africa are trained using Perold trellis systems. The initial Perold systems consisted of fixed foliage wires, but over the course of time these were replaced with moveable foliage wires to ease the task of shoot positioning. The larger hedge systems contain mostly

A prerequisite for the positioning of shoots is that there should not be too many thereof; it has been determined that ideally 16 to 24 shoots per running metre cordon are sufficient. This system has worked well in the past and very good results are still being obtained. It has been proven that the vine can compensate if suckering is performed early and that crop losses do not occur over time. The situation has changed however, and for certain wine objectives like bulk and entry-level wines, very little suckering is applied nowadays. The result is much more shoots per vine and subsequently shoot bundling occurs if everything is positioned. This then leads to poor aeration and compaction. Photo 1 is an example of a dense canopy with the characteristic appearance of yellow leaves.

Figure 1. Trellis systems 2009 vs 2019 (SAWIS)

10000 15000 20000 25000 30000 35000 40000 45000

41569

39347

39073

37097

15012

10338

4830

3307

0 5000

1020

719

312

259

156

116

74

74

25

0

0

0

Hedge

Perold

Bush vine Horizontally divided

Other

Vertically divided

Lyre system Guyot

Hedge (mechanical pruning)

Staked vine

2009 Hectares

2019 Hectares

FIGURE 1. Trellis systems 2009 vs 2019 (SAWIS).

WINETECH TECHNICAL YEARBOOK 2021 | 136