Impact of Yield Management Practices on Vine Growth and Fruit Composition of Oregon Pinot Noir

Premium wine grape production requires yield management practices to achieve quality. The majority of Oregon producers (89%) conduct crop thinning to reduce yields, and it is typically conducted from fruit set to lag phase. With rising production costs, growers are questioning current crop thinning practices. Research was conducted in two Pinot noir vineyards, one in the north Willamette Valley and another in the warmer region of southern Oregon’s Illinois Valley, during 2011 and 2012. The study evaluated crop thinning at three levels (0%, 40%, and 60% crop reduction) and four time points (pre-bloom, fruit set, lag phase, and véraison). Intensity of crop thinning had a greater impact on basic ripeness (SS, pH, and TA) and on total anthocyanin concentration than timing. Crop thinning by ~40% each year resulted in an increase in anthocyanins in the northern vineyard. Timing, not intensity, had an impact on anthocyanins in the southern vineyard during year 1 with 12% higher anthocyanin at véraison compared to thinning at pre-bloom and fruit set. Crop thinning by 60% did not further increase maturity nor result in higher anthocyanin, phenolic or tannin concentration compared to 40% thinning at either vineyard. The yeast assimilable nitrogen (YAN) concentration was influenced by intensity and timing of crop thinning for only the southern vineyard. The YAN was 41% higher in the pre-bloom thinned fruit (186 mg/L) compared to later time points (132 mg/L) in year 1. In year 2, early season thinned fruit was 51% higher in YAN than in the unthinned treatment, and thinning ~60% increased YAN by 49 mg/L. Despite differences in YAN, there was no difference in leaf blade or petiole N measured at véraison in either vineyard. Increasing crop level did not have major impacts on vine vegetative growth. No differences were found for whole vine leaf area or dormant pruning weights for the northern vineyard.  The southern vineyard had fewer laterals and lower pruning weight following year 2 for unthinned vines. Differences in vine growth and fruit composition observed in the two vineyards is likely due to differences in climate and vine balance, as the southern site had a wider range of  Ravaz Index (1.7 to 9.6) compared to the northern site (0.4 to 3.0). Despite different crop levels between years and location, crop thinning more than 40% of the crop in either vineyard did not enhance fruit composition for parameters measured.