Cluster thinning is a practice widely used in the context of fine wine production in South Africa. It effectively manipulates the leaf area-to-crop ratio and achieves balance between reproductive and vegetative growth. Additionally, it allows producers to attain more even ripeness by selectively removing lagging or later-ripening clusters. Over the years, extensive research has been conducted to determine the optimal timing and severity of cluster thinning that lead to the most desired and improved fruit composition. The objective of this study was to ascertain whether the timing of cluster thinning (bloom, pea size, lag phase, and veraison) or its severity (15 -35%, 36 – 55%, and 56-75%) influences yield and fruit composition.
Project Layout
A meta-analysis was conducted, scanning 160 research papers on cluster thinning. These articles spanned the period from 1970 to 2020 and were published in peer-reviewed scientific journals. The papers were narrowed down to 78 studies that met the desired criteria from which findings could be reported and utilized in this study. Criteria included only vinifera cultivars for wine production, correct measurement parameters, appropriate experimental design, publication in an academic journal, reporting of grape quality data, entire cluster thinning only, manual thinning (not mechanical), in-field trials only, and thinning only between pre-bloom and veraison.
Results
- While meta-analyses provide a large-scale view spanning multiple studies, they have drawbacks.
- Boundaries used to separate timing and severity treatments were determined subjectively and may convolute results.
- There is also an inability to account for the interaction between the timing and severity of treatments.
- Cluster thinning timing showed little influence on fruit composition.
- Moderate cluster thinning (36 – 55%) increased TSS and pH.
- The influence of cluster thinning on fruit composition was strongly moderated by cultivar.
- The climate was found not to be impactful.
- Cluster thinning effects on grape and wine aroma volatiles significantly improved more than basic fruit composition improvements.
Significance of the study
The beneficial effects of cluster thinning depend more on the severity of the action rather than timing. They are also cultivar-dependent. The cost of cluster thinning and the reduction in crop obviously have the potential to reduce vineyard profitability. Therefore, the cluster thinning practice should be performed in vineyards where clear quality and wine price point targets are defined.
Reference:
VanderWeide, Joshua, Nasrollahiazar, Esmaeil, Schultze, Steve, Sabbatini, Paolo, Castellarin, Simone Diego, Impact of Cluster Thinning on Wine Grape Yield and Fruit Composition: A Review and Meta-Analysis, Australian Journal of Grape and Wine Research, 2024, 2504396, 20 pages, 2024. https://doi.org/10.1155/2024/2504396