How to modulate mechanical winter pruning according to the productive and enological traits of four Vitis vinifera L. varieties cultivated in the north of Italy

The mechanization of winter pruning has been extensively used to reduce the labour requirement of a time-consuming operation, but if not adequately applied, it may lead to over-cropping and detrimental effects on grape quality. Considering the impact of mechanical winter pruning on vine performances, the present study was aimed to assess the appropriate level of mechanization of this technique on four cultivars, grown in distinct areas of the Emilia-Romagna Region (Italy) and characterized by different basal node fruitfulness and enological goals. The trial was conducted on the white cultivars ‘Trebbiano romagnolo’ and ‘Pignoletto’, both marked by low basal node fruitfulness and used for the production of table and sparkling wines, respectively. The evaluation was also conducted on the black cultivars ‘Sangiovese’ and ‘Lambrusco Salamino’, characterized by high basal node fruitfulness and usually assigned to the production of premium and sparkling wines, respectively. The compared pruning treatments were: a) manual pruning performed from the ground; b) mechanical pre-pruning and simultaneous manual follow-up performed with pneumatic shears from a tractor-drawn platform; c) mechanical pruning without manual follow-up. The latter treatment was not applied on ‘Sangiovese’ and ‘Lambrusco Salamino’ because previous studies demonstrated that hand finishing is necessary to prevent over-cropping in cultivars with high basal node fertility. The increase of bud load due to the manual follow-up after mechanical pre-pruning determined a higher yield increase in ‘Sangiovese’ and ‘Lambrusco Salamino’ rather than in ‘Trebbiano romagnolo’ and ‘Pignoletto’, however, no significant reduction of sugar concentration was observed in any cultivar. Conversely, sugar concentration was reduced by the mechanical pruning without hand finishing in the white berry cultivars, due to the excessive crop load. This study demonstrated that mechanical pruning with simultaneous manual follow-up may reduce up to 70% of labour requirements and that this operation may become a powerful tool to optimize yield without detrimental consequences on grape quality.