From 13th to 15th May 2022, the IX National Viticulture Conference (CONAVI) was held at the former monastery of San Francesco in Conegliano Veneto (TV), organised by the viticulture working group within the Società di Ortoflorofrutticoltura Italiana (SOI). As part of the congress, Tommaso Frioni presented a report on the use of the early defoliation technique to improve the suitability for drying of Santa Maria grapes, an autochthonous Piacenza variety used to produce Vin Santo di Vigoleno. The activity, carried out within the framework of action 5 of the plan, at the Azienda Agricola Lusignani di Vigoleno (Vernasca, PC), aims to develop an innovative protocol for managing the vineyard and the drying phase, according to the specific characteristics of the minor varieties used in the area. Santa Maria and Melara can in fact present compact bunches and thin-skinned grapes, which are often subject to rot both in the field and later in the drying rooms. In particular, the trial showed that a defoliation of the 6 basal leaves carried out pre-flowering (Fig.1) reduced fruit set from 42 to 33%. This in turn reduced bunch firmness, which was less susceptible to rot. The reduction in fruit set and in the number of berries per cluster did not lead to a reduction in yield since, due to a compensating effect, the berries in the defoliated plants were larger (Table 1). At harvest, the grapes from the plants subjected to early defoliation had more sugars than the control, and an unchanged titratable acidity. During the drying process, they showed a higher daily dehydration rate due to their larger size and reduced firmness, which favoured transpiration in the first 20 days after harvest (Chart 1). At 60 days, the grapes from the defoliated thesis had more sugar and more titratable acidity (Graph 2). The spread of rot was minimal in both theses, as the season was very dry and the grapes were in excellent condition at harvest The work will continue in 2022, in order to validate the preliminary results of 2021, and with the aim of evaluating in more detail any different susceptibility to rot.
Fig. 1 Santa Maria vines subjected to pre-flowering defoliation
Fig. 2 Santa Maria bunches of plants subject to early defoliation (left) and control plants (right)
Table 1 Yield and production components
Diagram 1 Development of berry water loss during the drying phases
Diagram 2 Evolution of sugars (left) and titratable acidity (right) during the drying phase