Mechanical winter pruning of grapevine: Physiological bases and applications

Since machine introduction in the early 1970s, much work has been expended to adapt pruners to vine trellis and physiological requirements, especially regarding the higher bud load their non-selective cuts leave compared to manual trimming. While units have successfully met the former requirement, efforts to meet the latter have been hampered by a broad range of variables depending on cultivar, machine type, environmental conditions and any manual follow-up. Several examples are instructive here. Winter hedge pruning usually delivers best results with low-to-medium basal node fruitfulness coupled with some hand finishing, two crucial factors for achieving the desired balance of crop yield and quality similar to hand pruning but at lower cost. Minimal pruning has by and large proved unsuccessful in European environments, although some of its good features like looser, less rot-susceptible clusters, earlier canopy filling, lower individual shoot vigor and higher vine capacity can be reproduced using a semi-minimal pruned hedge (SMPH) system to better control over-cropping while maintaining desired grape composition. For instance, the best option for winter mechanical pruning in Italian districts today is the single high-wire cordon managed to maintain upright canopy growth for fast and physiologically sound cutter-bar pruning with little or no manual follow-up. A more comprehensive outlook seems to presage robotics for "precision" pruning to deliver a bud load that is adjusted to vine vigor and desired crop level.