Rootstock Interactions with Cultural Practices
Cabernet Sauvignon grown on four rootstocks (3309, 5-C, 110R, and 039-16) were balance pruned to four different pruning formulae and examined for effects on yield, vegetative growth, and fruit maturity. Optimal pruning formula for each rootstock was determined for four different growth parameters. Maturation was dependent on total crop load per vine. Higher pruning formulas delayed maturity both directly and through influences on crop. Soluble solids at harvest were 24.9, 24.4, 24.3, and 23.9 °Brix for the 5, 7.5, 10, and 12.5 bud/lb treatments, respectively. Rootstock appeared to have a direct influence; at average crop loads, fruit ripened earlier if planted on 3309 and later if planted on 039-16. The natural delay in maturity of vines planted on 039-16 was mitigated in some years by low crops on that rootstock. Vines produced lower yields on 039-16 than on other rootstocks: 5.2, 6.5, 7.2, and 7.8 kg/vine for 039-16, 3309, 5-C, and 11 OR respectively. The responsible components were fewer clusters per shoot and fewer shoots per vine at any given formula. Pruning formula affected all components of yield except berry weight. Increases in buds retained at successively higher formulas resulted in more shoots and more clusters per vine but reduced bud viability and reduced clusters per shoot. The net effect was an increase in yield from 5.7 to 6.2, 7.2, and 7.7 kg/vine at the 5, 7.5, 10, and 12.5 bud treatments. Larger initial vine sizes increased yield through number of shoots per vine. Vines produced shorter shoots on 039-16 and 5-C than on 3309 or 11 OR. By the third year of study, vines on 039-16 also carried fewer shoots resulting in large differences in total leaf area per vine. Total average leaf areas were 6.7, 8.1, 9.1, and 9.8 M2/vine for 039-16, 5-C, 3309, and 110R. Higher pruning formulas increased shoot number but proportionately decreased shoot length and bud viability. Average total leaf area per vine therefore did not differ by pruning formula. Larger initial vine size increased total leaf area/vine through increased shoot number but did not affect shoot elongation. Pruning formula, not total shoots per vine, regulated vigor. Two measures of vigor and two measures of crop/vegetative balance were examined as criteria in assigning an optimal pruning formula to each rootstock. The formulas required to produce uniform shoot vigor were 8.9 buds/lb for 3309 and 110R, 8.1 for 5-C, and 8.0 for 039-16. Formulas necessary to produce uniform crop/vegetative partitioning averaged 10.4 buds/lb on 3309, 9.0 on 039-16, 8.5 on 110R, and 6.4 on 5-C.