Forcing vine regrowth and shifting fruit ripening in a warm region to enhance fruit quality in 'Cabernet Sauvignon' grapevine (Vitis vinifera L.)

In warmer regions, winegrapes ripen their fruit during the hottest portion of the growing season, producing wines of high pH, low acidity, less intense colour, and a less complex flavour. Experiments were conducted in a commercial vineyard of 'Cabernet Sauvignon' at Fresno, CA, USA in 2009, and in 2010, to determine if vines could be forced to enhance fruit quality. Forcing was conducted by hedging growing shoots to six nodes and removing summer laterals, leaves, and primary clusters between 14 - 70 d after anthesis in late-May, June, and July. Vines grown under conventional practices were used as controls. Forcing in June shifted fruit ripening from the hot (July and August) to the cool (October through early-November) portion of the growing season, a period with more hours at lower, more favourable temperatures. Fruit from the forced crop had smaller berries, a lower pH, higher acidity, and higher contents of anthocyanins, tannins, and total phenolics, compared with non-forced fruit. The yield and vigour of forced vines were comparable to, or slightly lower than, control vines. The best forcing treatment consisted of hedging growing shoots to six nodes and removing summer laterals, leaves, and primary clusters. Our study demonstrates the potential of forcing to address the detrimental effects of high temperatures on fruit quality in warmer regions of winegrape production.