Effect of timing and intensity level of cluster thinning on yield and quality of cv. merlot (Vitis vinifera L.) grown on a big t trellising system

This research was conducted in the vineyards owned by Denizhan Kalaylıoğlu, located at an elevation of 65 meters between the coordinates 39°48'03" N and 26°22'01" E in the village of Güllüce, which is affiliated with the Ezine district of Çanakkale province. The experiment was established on 12-year-old Merlot grapevines grafted onto 41B rootstocks grown in the vineyard, with the aim of determining the effects of cluster thinning at different times and levels on yield and quality. The trial was carried out for two years during the vegetation periods of 2020-2021 and 2021-2022. The study involved 6 different phenological stages: pre-bloom, berry set, pea-sized berries, veraison, half ripening and pre-harvest. Along with these stages, 3 different levels of cluster thinning were applied: 0% (control), 25% cluster thinning, and 50% cluster thinning. The effects of these applications on berry characteristics (berry width-length, fresh-dry weight, volume, etc.), cluster characteristics (cluster width-length, weight, compactness, etc.), must characteristics (total soluble solids, total acidity, pH, anthocyanin, TPI, etc.), and yield parameters (per vine and per hectare) were investigated. Regarding berry characteristics, seasonal differences were observed, and it was determined that cluster thinning was more effective compared to the control. In terms of cluster characteristics, it was noted that thinning during the berry set period increased the evaluated criteria. During the berry set and veraison periods, it was found that 50% cluster thinning improved both yield and quality. As a result, for the Merlot grape variety under the conditions of the Ezine district in Çanakkale province, it was concluded that cluster thinning at a 25% level during the veraison period is more feasible for commercial and high-quality production.