Intensity and timing of defoliation on white cultivar Chasselas under the temperate climate of Switzerland

Abstract

Aim: The objective of this work is to evaluate the pre-berry-set defoliation on the white cv. Chasselas as a potential vineyard practice in Switzerland, with particular attention to the impact of defoliation intensity on the yield and wine sensory parameters. Methods and results: Defoliation (removal of 6 basal leaves + 6 lateral shoots per shoot) was completed during three developmental stages of grapevine, i.e., pre-flowering, flowering and bunch closure, and at two intensity levels (50 and 100 % of the fruit zone). The experimentation was performed repeatedly over four years. In addition to vintage effect, pre-flowering defoliation had a consistent impact on vine agronomic behaviour. The yield was highly affected by the technique (more than 30 % loss). Earlier and more intense defoliation had more impact on yield, while post-berry-set defoliation had no effect on yield. Pre-floral defoliation affected bud fruitfulness and vigour, i.e., trimming and pruning weights. This result noted a carryover effect that could affect vine sustainability under restrictive conditions. Pre-floral defoliation also increased berry skin thickness and had a positive impact inhibiting Botrytis development. However, white wine composition and sensory analysis were not affected by the practice, provided that a sufficient leaf-to-fruit ratio is maintained to guarantee a proper grape maturation. In terms of methodology, the environmental scanning electron microscopy (ESEM) represented an interesting alternative to conventional transmission electron microscopy (TEM) to observe berry epidermis, as it is less time-consuming. Conclusion: In the context of this study, pre-flowering defoliation seems to be an interesting practice to reduce vigour and control the high production potential of the cv. Chasselas, without affecting wine sensory parameters. The intensity of early defoliation allows for the modulation of the impact on the yield in order to prevent excessive yield loss. Significance and impact of the study: Pre-flowering defoliation of white cultivars represents a prophylactic solution to reduce both chemical entrants and bunch-thinning costs.