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74 WINES&VINES February 2017 GRAPEGROWING PRACTICAL WINERY & VINEYARD tions of EL stages (see "Median Bloom and Véraison Dates for Treatment-Pruning Combina- tions"). Bloom occurred between 15 and 17 days earlier for clusters on shoots from spurs pruned early (January) compared to those from spurs pruned later (March). The median data of véraison (EL 38 or 50% berry colored) was also extrapolated from weekly observations of EL stages for the treatments. In all cases, clusters on late-pruned spurs reached the EL Stage 38 earlier by six to seven days than clusters on early pruned spurs. The phenological differences at véraison were easily observed in the vineyard (see photos on page 75). The differences in the onset of véraison were large enough to demonstrate which clusters would probably be re- moved during green drop (fruit on late-pruned spurs) if a pass was scheduled at that time. A o n e - w e e k d i f f e r e n c e i n t h e onset of véraison appears to be s u f f i c i e n t f o r c o n s i d e r i n g a green thinning pass. The bene- fits of green thinning in terms of improved uniformity of ripe- ness must be weighed against the labor cost of a green thin- ning pass and the amount of crop loss. In this trial, green drop of fruit on late-pruned spurs would result in a yield reduction of approximately 50%, which may not be economically justified. The variability in fruit ripeness generated by differential prun- ing is probably greater than nor- mally encountered in vineyards, however it demonstrates the level of asynchronous shoot and c l u s t e r d e v e l o p m e n t t h a t i s possible. Variability of shoot phenology around véraison can be repre- sented using a box-and-whisker plot (see "Phenological Stage Variability by Treatment" on page 74). The box represents the EnartisUSA_OakAlternatives tr.indd 1 25/02/16 10:51 Promote your wines to leading Zinfandel enthusiasts and extend your winery's relationship in the market. Join Us! We are champions of Zinfandel— America's Heritage Wine Become part of our proud legacy zinfandel.org • 530-274-4900 Zinfandel Advocates & Producers is a 501(c)(3) non-profit organization. ZAP is dedicated to advancing public knowledge of and appreciation for American Zinfandel and its unique place in our culture and history. You know how good your Zinfandel is... MEDIAN BLOOM AND VÉRAISON DATES FOR TREATMENT-PRUNING COMBINATIONS Treatment Bloom (EL 23) Véraison (EL 38) Early Late Early Late Separate Vines May 8 May 23 July 24 July 31 Opposite Cordon May 8 May 23 July 25 July 31 Alternate Spurs May 6 May 23 July 25 July 31 The bloom and véraison dates for shoots on early and late-pruned spurs was extrapolated from the weekly observations of EL stages. PHENOLOGICAL STAGE VARIABILITY BY TREATMENT Box and whisker plots of EL stages for early and late-pruned shoots on separate vines (SV), opposite cordons (OC) and alternate spurs (AS) on July 28, 2015. SV Early SV Late OC Early OC Late OC All AS Early AS Late AS All Modified EL Stage 41 40 39 38 37 36 35 34 33