Factors influencing grapevine vigour and the potential for control with partial rootzone drying

Maintaining the most cost-effective balance between vegetative and reproductive growth is one of the most testing problems in modern viticulture. Grapevines which exhibit excessive vegetative vigour are likely to produce less fruit of reduced quality, and vines with inadequate vigour may be compromised in terms of their yield potential. The requirement for techniques to better manage excess vigour has become more acute in recent years with the increased use of irrigation, adoption of vigour-imparting rootstocks and the expansion of vineyards into cooler geographic regions. A number of strategies may be used to control vine vigour. Chemical growth regulators, although capable of reducing shoot vigour, have never received acceptance due to undesirable side effects and concerns over chemical residues. Devigorating rootstocks, likewise, may have the potential to control vigour but none are in wide commercial use. Restriction of the effective root volume, achieved through manipulation of planting densities, competition by cover crops, regulation of the soil volume wetted by drip irrigation or regulation of water availability can all achieve a degree of devigoration but often at the expense of fruit yield. Manipulation of vines through pruning and trellis design are probably the most commonly used methods for the control of shoot vigour. A high number of nodes retained at pruning combined with trellises which allow open canopies have proved successful. Advances in the understanding of the physiological factors influencing shoot growth and transpiration have allowed the development of novel irrigation methods for the control of vine vigour. These techniques exploit the fact that chemical signals originating in the roots are primarily responsible for the control of shoot growth and transpiration. Stimulation of the production of these signals through partial drying of the root system results in a significant reduction in shoot growth and water-use while maintaining crop yield and improving fruit quality. These new techniques, in combination with appropriate pruning and trellising methods, are providing new viticultural tools for controlling vine vigour and water-use efficiency.