Browsing by Author "Wolf, T. K."

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    Cover Crop, Rootstock, and Root Restriction Regulate Vegetative Growth of Cabernet Sauvignon in a Humid Environment
    Hatch, T. A.; Hickey, C. C.; Wolf, T. K. (American Society for Enology and Viticulture, 2011-09)
    Cover crops, rootstocks, and root restriction were evaluated as means to regulate vegetative growth of Cabernet Sauvignon grapevines in a humid environment. Treatments were arranged as a strip-split-split plot with row-middle and under-trellis cover crop (UTCC) compared to row-middle only cover crop combined with 85 cm weed-free strips in the vine row as main plots. Rootstocks Riparia Gloire (Riparia), 420A, and 101-14 were subplots, while sub-subplots comprised two treatments: vines were either planted in root-restrictive (RR) fabric bags (0.015 m(3)) at vineyard establishment or were planted without root restriction. Root restriction and UTCC were independently effective in suppressing vegetative development as measured by rate and seasonal duration of shoot growth, lateral shoot development, trunk circumference, and dormant pruning weights. Riparia was the most effective rootstock in limiting vegetative development among the three evaluated; vines grafted to Riparia had similar to 25% lower cane pruning weights than did vines grafted to 420A or 101-14. Under-trellis cover crop reduced cane pruning weights by 47% relative to vines grown on herbicide strips. Canopy architecture was generally improved by both UTCC and by root restriction, but generally unaffected by rootstock. Root restriction reduced the discrimination against C-13 assimilation in both berries and leaf laminae tissue as measured by delta C-13, while under-trellis floor management did not affect this measure of chronic water stress. The principal direct effeci of the UTCC and the root-restriction treatments was a sustained reduction in stem (xylem) water potential (psi(stem)). Stomatal conductance and net assimilation rate were depressed by increasing water deficit, particularly for root-restricted vines. Results suggest practical measures can be used to create a more favorable vine balance under conditions of variable rainfall, such as exist in the eastern United States.
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    Effect of vertical shoot-positioned, smart-dyson, and Geneva double-curtain training systems on Viognier grape and wine composition
    Zoecklein, Bruce W.; Wolf, T. K.; Pelanne, L.; Miller, M. K.; Birkenmaier, S. S. (American Society for Enology and Viticulture, 2008-03)
    Viognier grapes grown in northern Virginia and resultant wines were evaluated as a function of training system. Treatments included vertical shoot-positioned (VSP), Smart-Dyson (SD), and Geneva double curtain (GDC), with vines of all treatments spaced 2.4 m apart in 3.0 m wide rows. In addition to increased cluster numbers and crop yield, GDC training generally increased fruit zone sunlight interception and fruit exposure, while it decreased cane pruning weights per meter of cordon, compared with SD and VSP. Crop adjustments were made between bloom and veraison in six seasons, to result in average yields of 10.5 kg/vine (GDC), 9.9 kg/vine (SD), and 6.0 kg/vine (VSP), with the lower SD canopy bearing 30 to 40% less crop than the corresponding upper SD canopy. Crop loads (yield/cane pruning weight) were generally between 4 and 12; GDC crop load approached 20 in three seasons, while SD approached 14 in one. Leaf area per crop ratio was determined one season and exceeded 1.8 m(2)/kg of fruit for all systems. Fruit was harvested at similar Brix values, with differences in berry weight, pH, titratable acidity, and malic and tartaric acids among treatments generally not significant. Volatile compounds were analyzed using headspace solid-phase microextraction GC-MS. Fruit showed consistent differences in linalool, alpha-terpineol, beta-damascenone, and n-hexanol concentrations among training systems. SD had the highest concentration of most free volatiles quantified in both juice and wines, while GDC wines frequently had the highest concentration of phenol-free glycosides. Triangle difference sensory testing demonstrated differences between GDC and SD in wine aroma and flavor and between VSP and SD in flavor. GDC wines generally had higher fruity and floral aromas compared with the other systems.
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    Reduction of bunch stem necrosis of Cabernet Sauvignon by increased tissue nitrogen concentration
    Capps, E. R.; Wolf, T. K. (American Society for Enology and Viticulture, 2000)
    Field experiments were conducted over three years at two vineyards in northern Virginia to examine relationships between specific nutrients and the incidence of bunch stem necrosis (BSN) of Cabernet Sauvignon. Nitrogen, magnesium, acid calcium were applied alone or in combination. Only one of the vineyards (Winchester) showed appreciable BSN incidence during the study period. During the 1996 season at Winchester vineyard, bloom-time leaf petiole and veraison rachis nitrogen concentration of unfertilized (control) vines were 0.80% and 1.16%, respectively. The corresponding control BSN incidence was 41% at harvest time. Seasonally split application of nitrogen fertilizer at 112 kg/ha actual nitrogen increased bloom-time leaf petiole and veraison cluster stem nitrogen concentration to 1.85% and 1.82%, respectively, in the nitrogen plots. The corresponding BSN incidence was reduced to 14% at harvest time. BSN symptoms were not as pronounced during the 1997 season; however, all treatments, including the control plots had elevated tissue nitrogen levels in 1997. Application of nitrogen fertilizer in 1998 was associated with bloom-time leaf petiole and veraison rachis nitrogen concentrations of 1.18% and 1.34%, respectively. Corresponding BSN was reduced to 3% at harvest time, versus 17% to 23% in treatments that did not receive nitrogen. Magnesium and calcium had minimal (1997) or no impact on BSN incidence. Measures of canopy density, cane pruning weights, crop yield, and fruit chemistry suggest that the ameliorating effects of nitrogen on BSN incidence were directly related to increased tissue nitrogen concentration, and not an indirect effect of vigor stimulation or crop ripening rate. A low incidence of BSN at the second vineyard precluded a definitive explanation of prior BSN expression at that location. We conclude that low tissue [N] may be one cause of BSN, and that vineyards should be examined individually for contributing factors.