The effect of canopy management strategies on the berry composition and harvest dates of Sauvignon blanc was investigated in a study performed by a New Zealand research group.

Introduction

The leaf area to fruit mass ratio is a source-sink ratio that may have an important influence on grape development and maturity during ripening. Both the leaf area, as well as the fruit mass, can be manipulated through viticultural practices such as leaf/shoot removal and crop thinning.

Materials and methods

The study was conducted in a commercial vineyard in the Wairau Valley, Marlborough, New Zealand. Sauvignon blanc vines (clone MS) were used in this trial. The canopy management strategies included:

  1. Trimming the shoots (no leaf removal in the bunch zone) to six or 12 main leaves per shoot, and/or
  2. Removing bunches (0, 50 or 75% bunch removal).

The canopy management strategies were applied either at fruitset or at veraison. The berry composition was monitored during regular intervals from pre-veraison to harvest and included total soluble solids concentration (TSS) (°Brix), pH, titratable acidity and fresh berry mass.

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Results

Reducing the leaf area

  • Reducing the leaf area to six leaves at fruitset (0% crop removal) had the most significant influence on the ripening tempo resulting in delayed veraison (up to one week).
  • The rate of TSS accumulation of the six-leaf treatment was significantly slower than when the leaf area was reduced to 12 leaves (0% crop removal).
  • Reducing the leaf area at veraison also slowed the rate of TSS accumulation during maturation; however, the effect was not as pronounced as when the leaf area was reduced at fruitset.

The two trimming regimes, therefore, resulted in very different ripening rates, with the effect being more pronounced when the canopy management strategy was applied at fruitset compared to at veraison. This would suggest that the earlier the trimming is applied, the greater the effect on the berry composition and ripening tempo. Care should be taken as the ability of the bunches to reach a targeted TSS concentration might be compromised in cases where severe trimming techniques were applied.

Crop removal

  • Crop removal (either at fruitset or veraison) resulted in higher TSS concentrations at harvest compared to 0% crop removal. This effect was seen for the majority of the shoot trimming treatments.

Therefore, crop removal accelerated the TSS accumulation rate regardless of the severity of trimming.

Leaf area reduction vs crop removal

Restricting potential carbohydrate sources (through shoot trimming) in Sauvignon blanc during post-flowering resulted in delayed veraison and maturation, while crop removal affected the evaluated parameters to a lesser extent. When the leaves were removed (six-leaf shoots) in combination with bunch removal (50% crop removal), a countereffect was observed, and the rate of TSS accumulation was similar compared to the 12-leaf shoots with 0% crop reduction.

Other ripening markers

Titratable acidity, pH and fresh berry weight were largely unaffected by the treatments. It is therefore possible to reduce the rate of TSS accumulation without altering the evolution of other ripening markers. However, the relative composition and relationship between the berry components must be considered when applying these ripening management strategies.

Conclusion

Canopy management practices such as shoot thinning, leaf removal, hedging and crop thinning are often used to modify the canopy for a specific target of shoot density, crop level, or cluster exposure. However, canopy management strategies such as leaf area reduction by trimming shoots and crop removal can also be successfully employed to adjust the rate of TSS accumulation, and therefore the timing of veraison and harvest dates.

It is possible to manipulate the TSS accumulation using canopy management techniques without affecting other ripening markers such as titratable acidity and pH. The extent to which the reduction in leaf area and crop removal alters the source-sink ratio in grapevines and subsequently changes TSS accumulation rates post-veraison largely depends on the degree and timing of crop removal and/or shoot trimming. The secondary effects of these canopy management strategies should be considered. For instance, shoot trimming early in the growing season could encourage lateral growth, causing the canopy density to increase.

Under warmer climate conditions, delaying veraison and slowing TSS accumulation could help address logistical issues during compressed harvests. This information is also potentially important to counteract the effect of advanced phenology in response to increased temperature due to climate change or, conversely, to enable target TSS concentration to be reached in marginal environments with cooler climates.

Abstract

Canopy management strategies such as crop removal and leaf area reduction by shoot trimming can be successfully employed to adjust the ripening tempo of Sauvignon blanc resulting in modified veraison and harvest dates.

Reference

Parker, A.K., Hofmann, R.W., Van Leeuwen, C., McLachlan, A.R.G. & Trought, M.C.T., 2015. Manipulating the leaf area to fruit mass ratio alters the synchrony of total soluble solids accumulation and titratable acidity of grape berries.Australian Journal of Grape and Wine Research 21(2), 266 - 276.

– For more information, contact Carien Coetzee at [email protected].

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