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76 WINES&VINES February 2017 GRAPEGROWING PRACTICAL WINERY & VINEYARD half the difference between aver- age values for both (0.5º to 0.7º Brix in this case). The effect may have little noticeable impact on overall wine quality later, espe- cially since pH and titratable acidity were no different be- tween clusters on early and late- pruned spurs. It is possible that the differ- ences in Brix would become less o r n o t e x i s t e n t a s r i p e n i n g reaches the limits of sugar load- ing in the berry, which is approxi- mately 25° Brix. In vineyards where extended hang time is practiced, the variability in Brix between clusters may not be as great as all the clusters have had time to reach limits of sugar accumulation. If little or no impact on must and wine composition or quality is to be realized from green thin- ning, then there may be little justification to do it. The labor cost and cost of yield reduction needs to be weighed against the possible benefits (if any) of a green-thinning pass. There is little evidence that uniformity of ripeness between clusters leads to better wine qual- ity. A recent study revealed that vineyards with high-value fruit in terms of potential wine quality had greater berry-to-berry and cluster-to-cluster variability in ripeness than vineyards with lower value fruit. 1 More research on the impact of green thinning on wine composition and quality is needed. Support for the assumption The results of this trial provide evidence for phenological shoot autonomy in grapevines. Sea- son-long persistent differences in phenology after bud break are to be expected, as shoots on the same vine appear to lack any ability to synchronize phe- nology later in the growing sea- son. Factors that contribute to uneven bud break could result in greater variability in ripeness between clusters on the same grapevine. Michael Sipiora is the regional viticultur- ist in Napa Valley for Treasury Wine Estates, and Amanda Cihlar is the direc- tor of vineyard operations at Hamel Family Wines. References for this article are available online at winesandvines.com. FRUIT MATURITY THREE WEEKS AFTER VÉRAISON Treatment Prune Brix pH TA (g/L) Separate Vines (SV) Early 21.9 3.32 7.13 Late 21.0 3.28 8.28 Opposite Cordon (OC) Early 21.8 3.30 8.60 Late 20.6 3.29 9.25 Alternate Spur (AS) Early 22.0 3.28 8.92 Late 20.4 3.30 8.90 Treatment ns ns * Prune Date *** ns ns Treat * Prune ns * ns Rep ns ns ns Late-pruned vines were observed to have a 1° to 1.5° lower Brix level on Aug. 26, 2015, three weeks after completing véraison.