Physiological response of winegrape to management practices for successful mechanization of quality vineyards

The viticulture of Italy's fertile Po Valley has been traditionally associated with tall, expansive training systems requiring about 400 man-hours of labour yearly per hectare, most being needed for hand harvesting and pruning. Pruning in these trellises (e.g. Capovolto, Raggi, Sylvoz) is based on long canes which are usually bent or arched severely. Such cane positioning often causes non-uniform shoot growth along the cane and staggered cluster ripening, which is an obstacle to mechanical harvesting. These factors, along with the increasing decline of the labour pool in Italy since the early 1970s, have led to the introduction in the Po Valley of the Geneva Double Curtain (GDC) trellis; a spur-pruned system featuring two parallel walls of downward growing shoots which can readily be machine harvested using a vertical shaker unit. As harvest mechanization of GDC has cut the yearly labor demand by about 50%, efforts were then concentrated on the mechanization of winter pruning. Long-term trials on machine-pruned GDC vines using a multiple cutter bar unit with or without hand finishing demonstrated that the hedged vines react to the increased node number retained by non-selective machine cuts with offset mechanisms such as lower budbreak, shoot fruitfulness and cluster weight, leading to unaltered yield and must quality. Moreover, adequate renewal of year-old wood was obtained because of the randomness of cut length along the cordon. Mechanization of pruning lowered the yearly labour demand in GDC to 71 hours per hectare, 30 % being needed for manual shoot positioning, a key operation for maintaining canopy division and improve light penetration and cluster exposure. More recently, a device has been designed to semi-mechanize shoot positioning in GDC, cutting annual labour demand to a minimum of about 55 hours/ha. Full mechanization of harvesting and pruning is also achieved with the free-cordon (FC) trellis, a spur-pruned, single hedgerow featuring no support wires. Unlike the GDC, FC does not require manual shoot positioning and is suitable to mechanical harvesting by any overrow machine with horizontal slappers. A modified version of the FC featuring trunk bending and moveable support wire has been designed to enable mechanical harvesting with vertical impactors. Mechanical pruning can be performed with the multiple cutter bar unit designed for the GDC, although this operation is greatly facilitated with cultivars having a natural semi-upright or upright growth habit. A trial conducted to compare FC and GDC has shown similar vine performance, although the FC vines had higher vigour. Both training systems are viable options in medium-to-high vigour areas where yield maintenance, high quality grapes and cost reduction are key factors in decision-making.