International Journal of Horticulture, 2025, Vol.15, No.6, 290-298 http://hortherbpublisher.com/index.php/ijh 291 molecular perspectives to account for the role of defoliation in the control of fruit quality and sugar accumulation (Doğan, 2025). This study summarizes the current application status of leaf picking, in the production of fresh table grapes, with a focus on discussing its impact on fruit quality and sugar accumulation. The content covers physiological, biochemical and molecular mechanisms, as well as the practical effects of different leaf-picking strategies. This study further emphasizes the importance of optimizing leaf-picking measures in table grape cultivation, and provides a reference for precise vineyard management and fruit quality improvement to meet the constantly changing market demands. 2 Fundamentals and Methods of Leaf Removal 2.1 Definition and common approaches of leaf removal Leaf removal, also referred to as defoliation or thinning of the leaves, is a farming technique in which there is selective removal of leaves from the grapevine canopy, but within the fruiting zone. The technique is primarily used to improve the microclimate surrounding the grape clusters for improved sunlight exposure and air movement, leading to improved quality of the fruit and reduced incidence of diseases. It can be mechanically or manually removed and is generally applied to basal leaves that cover up clusters, with the specific practice varying depending on purpose and vineyard conditions considered (VanderWeide et al., 2021; Doğan, 2025). 2.2 Straw yield The removal rate is generally classified as light, moderate, or heavy, depending on the percentage of leaves taken off the canopy. Light removal takes off a few leaves and causes minimal change in the canopy structure. Moderate removal typically takes off several leaves per shoot, especially those immediately above the fruit zone, and is commonly used to maximize fruit exposure and vine vigor. Heavy removal refers to the removal of a significant number of leaves, potentially significantly altering the source-sink regime of the vine. Although moderate removal is most commonly associated with optimal improvement in grape quality, heavy removal might subject vines to overexposure, sunburn, or reduced yield, and hence should be exercised with extreme caution (Aipperspach et al., 2020). 2.3 Effects of different removal positions The date of leaf removal is significant in determining its effect on grape quality. Basal leaf removal, or removal of leaves close to the base of shoots and surrounding the clusters, is the most popular practice and is shown to be successful in facilitating sunlight exposure, increase phenolic and anthocyanin accumulation, and reduce disease pressure. Removal of middle or upper canopy leaves is not often utilized but may be an option on some training systems or to even further open the canopy. Cluster-zone leaf thinning, for the leaves immediately surrounding the fruit clusters, has also been shown to be particularly effective in improving microclimate conditions for berry growth, promoting sugar uptake, and boosting synthesis of aroma and pigment compounds while exercising care to avoid over-exposure (Tarricone et al., 2020; Quartacci et al., 2022). 2.4 Timing of leaf removal When to drop the leaves is a crucial aspect in modifying its impact on grape quality and growth. Early defoliation, practiced before or at flowering, can potentially lower compactness of bunches and disease pressure, and overall be associated with more sugar and phenolics, though yield will be lowered through less fruit set (Sivilotti et al., 2016; VanderWeide et al., 2021). Leaf removal during berry growth (fruit set to veraison) may enhance color and volatile development with less risk of fruit loss, while leaf removal later during ripening (veraison to harvest) may enhance color and phenolics with more risk of sunburn and less effect on sugar content. The choice timing should be adjusted according to the corresponding cultivar, climate, and production target (Yue et al., 2020a; Quartacci et al., 2022).
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