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52 WINES&VINES June 2017 GRAPEGROWING PRACTICAL WINERY & VINEYARD yields were similar and small berries were achieved without the penalties that accompa- nied the severe deficit treatment. Although both the ET 25 and ET25/100 vines received the same amount of water early in the season, the ET 25 treatment had smaller berries than the ET25/100 vines. One explana- tion for this is that the 100% ETc supplied at véraison may have alleviated pre-harvest berry dehydration. 12 Additionally, because the increase in water occurred when berries ranged from blue to green, research from Keller's group suggests that photosynthetic recovery following the increased water supply may increase sugar supply via phloem flow to the berries. 13 In- deed, total soluble solids (berry sugars) were intermediate in the ET25/100 vines (242 mg) compared to 213 mg for ET 25 and 282 mg for ET 70 or ET 100 . Deficit irrigation without yield penalties Though moderate water deficit in red wine grapes is generally associated with positive attributes such as fruitier and less vegetal aromas, more anthocyanin pigments and sometimes lower astringency when compared to vineyards where abundant water is ap- plied, 13 the research showed there can be too much of a good thing when it comes to water stress and wine grapes. Supplying only 25% ETc between fruit set and harvest was too low, economically unsus- tainable and led to a decline in vine capacity and yield, according to the report. The 25% ETc vines had the most open canopy and consequently the highest cluster temperatures of the four irritation treatments, the greatest light intensity in the fruit zone and the small- est yield (almost half of the other regimens in two of the three years). "By contrast, limiting water to 25% ETc early during the berry-development period and then increasing it to 100% ETc at véraison proved to be an interesting irrigation-manage- ment option for Cabernet Sauvignon," the re- port states. This treatment limited vigor and berry size while keeping yields moderate—and without the penalties as in the severe deficit treatment. Moreover, the ET25/100 treatment conserved irrigation water. An indirect benefit of using less water than ET 100 was weed control. Although this study did not quantify weed growth, visual observations found more abun- dant weeds in the fully watered vines of ET 100 compared to other treatments. With its mea- ger application of water from after fruit set to véraison, the ET25/100 treatment may be a way to reduce weed growth and the need for herbicides or cultivation. How low can you go? While earlier field trials by the same re- searchers had found that 35% ETc is via- ble, 4,10 the present work established that 25% ETc is not economically sustainable in the arid climate of eastern Washington, where the study was conducted. The results of this study help to better un- derstand the role that deficit irrigation plays in fruit quality. Small berry size is often cited as the primary reason for fruit composition im- provements made by water deficit. But this study suggests that potential changes in fruit composition due to water deficit may be indi- rectly related to altered canopy size and micro- climate, in addition to decreased berry size. Melissa Hansen, research program manager for the Washington State Wine Commission, grew up in Cali- fornia's Central Valley and worked in California's grape and tree fruit industries before moving to Washington. She covered grapes and tree fruit for the Yakima, Wash.- based Good Fruit Grower magazine for 20 years before her current position. The references for this article are available online at winesandvines.com