Abstract:
Background and Aims: Controlling crop yields, fungal rot incidence and improving the quality of grapes and wines in an economically feasible manner, is an integral aim of modern viticulture. Pre-veraison defoliation is a technique which has shown significant promise in achieving these aims in Studies conducted in warm climate viticultural regions, and thus the aim of this investigation was to investigate the feasibility of its application in the cool climate viticultural region of New Zealand's Hawke's Bay. Methods and Results: Pre-veraison defoliation was investigated in four varieties of Vitis vinifera, Chardonnay, Sauvignon blanc, Merlot and Cabernet Sauvignon. Seven treatments were conducted in each variety in triplicate, hand and mechanical defoliations conducted at each Pre-Anthesis, Fruit Set, and Pre-Bunch Closure, while a non-defoliated treatment was also included as the control. The parameters assessed as a part of this study included crop yield and mean berry weight, rot incidence, cluster compactness and grape and wine chemical composition. Pre-veraison defoliation conducted both by hand and mechanically proved to be effective at reducing crop yields and rot incidence, however mean berry weight and cluster compactness were generally not affected. Some increases were observed in grape chemical composition; however these were not as profound as those observed in crop yields and rot incidence. Importantly, no reductions in the concentration of those compounds correlated with quality were observed. Conclusions: In the cool climate viticultural region of New Zealand's Hawke's Bay, pre-veraison defoliation conducted by either hand or machine has been indicated to be an effective mechanism for reducing crop yields and reducing fungal rot incidence. Pre-veraison defoliation may also act to increase the concentration of some compounds correlated to quality. Importantly pre-veraison defoliation was shown not to detrimentally affect the composition and thus potential quality of the grapes and wines produced from plants in which it was conducted.
