Cluster Thinning Reduces the Economic Sustainability of Riesling Production

Crop levels of 1 (low), 1.5 (medium), and 2 (high) clusters per shoot established by cluster thinning (CT) were compared to nonthinned (control) Riesling vines over a three-year period. Yields ranged from 5.2 to 12.4 t/ha in 2008 and from 4.0 to 9.3 t/ha in 2009, while crop loads (yield/pruning weight) ranged from 2.9 to 8.7 in 2008 and 2.9 to 9.9 in 2009. By 2010, yield and crop load (yield/pruning weight) did not differ among treatments. Cluster weight was unaffected by CT in 2008 and 2009 but in 2010 control clusters weighed 39% less than low crop. There was little or no CT effect on berry size, pH, titratable acidity, pruning weight, cluster light exposure, or bud cold hardiness. Soluble solids at harvest ranged from 18.2 Brix in control to 22.3 Brix in low crop in 2008, from 18.9 to 22.1 Brix, respectively, in 2009, and from 20.5 to 22.0 Brix, respectively, in 2010. A consumer wine aroma sorting trial revealed that the low crop wine, and the low and medium crop wines, differed in aromatic attributes from the other treatments in 2008 and 2009, respectively. Grower financial net return per hectare ranged from $2,832 in low crop to $16,055 in control in 2008, from −$115 to $8,596, respectively, in 2009, and from $1,938 to $4,242, respectively, in 2010. Financial losses associated with CT could be recouped only by increases of up to 143% over base market price for grapes.