Thinning intensity and water regime affect the impact cluster thinning has on grape quality

Late cluster thinning is a practice frequently used in the vineyards of semiarid regions, as it is claimed to increase total soluble solids and anthocyanin concentration. However, when performed in field conditions, it often leads to relatively inconclusive results: under some circumstances, it results in a noteworthy quality gain, whereas under other circumstances, it does not convey the improvement in quality desired. The aim of this work was to evaluate the influence of thinning intensity and vine water status on the impact cluster thinning has on grape quality. Late cluster thin ning (CT) was performed at four 'Tempranillo' vineyards during four consecutive years. The major effects of CT were an increase in berry soluble solid, anthocyanin and phenolics concentration. The impact CT had on these parameters was related to thinning intensity, although it was more closely related to vine water status of from veraison to harvest, particularly when compared to water status during the two weeks with the lowest water availability. An estimation of the degree of water deficit that is likely to occur between veraison and harvest (considering water management guidelines of each winegrower and water reserves available in the soil or for later irrigation) has therefore to be considered in order to make proper decisions on cluster thinning, at least in the range of yield and water conditions included in this study. In rain fed or deficit irrigated vineyards water deficit alleviation might be one of the main mechanisms that make cluster thinning an effective technique to improve grape quality.