An estimate of the amount of clusters that a vine can reasonably bring to maturity is essential for optimizing crop level. This work was conducted to determine whether the timing of maturity in a high-yielding, dry-farmed Vitis vinifera L. Cabernet Sauvignon vineyard could be manipulated through rootstocks and crop level. Cabernet Sauvignon, grafted on 5C Teleki (V. berlandieri Planch. x V. riparia Michx), 1103 Paulsen, 140 Ruggeri, and 110 Richter (V. berlandieri Planch. x V. rupestris Scheele), was used in a trial carried out in 1997 and 1998 in an 8-year-old vineyard near Oakville, California. Four levels of crop were imposed by winter pruning all vines to four-bud spurs and cluster thinning at veraison: treatment 1 (100%), or double crop, no thinned vines with ~26 shoots and 40 clusters per vine; treatment 2 (75%), in which 25% of clusters were thinned; treatment 3 (50%), the standard crop level in the study area or control, in which 50% of clusters were thinned and one cluster per shoot was retained; and treatment 4 (25%), in which 75% of clusters were thinned and one cluster every two shoots was retained. The time required to reach 23.5, 24.0, and 25.0 Brix was linearly dependent on crop level with a rate of about one day per each ton of grapes. Rootstocks and crop levels had no or little impact on fruitfulness, cluster and berry size, and final Brix. The reduction in sugar accumulation seems to be a sensitive measure for crop level and does not appear to be influenced by rootstock or environmental conditions.
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