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 ~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 13 C assimilation in both berries and leaf laminae tissue as measured by δ 13 C, while under-trellis floor management did not affect this measure of chronic water stress. The principal direct effect of the UTCC and the root-restriction treatments was a sustained reduction in stem (xylem) water potential (ψ 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.
Angiosperms are well adapted to tolerate biotic and abiotic stresses in their native environment. However, the growth habit of native plants may not be suited for cultivation and their fruits may not be desirable for consumption. Adapting a plant for cultivation and commercial appeal through breeding and selection may accentuate weaknesses in pest tolerance. The transition of muscadine from a wild, native plant to a cultivated crop has taken place over the last 150 years. Early production primarily involved cloning elite wild selections; few pest management inputs were needed since the material was genetically similar to the native plant. Over time, emphasis was placed on the refinement of pruning, trellising, and other cultural inputs to increase productivity and commercial implementation. In turn, breeders developed newer cultivars with greater productivity and commercial appeal. Many modern muscadine cultivars remain tolerant to biotic pests and are adapted to a hot and humid climate. The primary focus of this review is to provide a descriptive context of muscadine as a native American, perennial fruit crop that requires minimal pest management in hot, humid climates relative to recently introduced European bunch grapes. Inherent muscadine traits resulting in fewer pesticide inputs make them worthy of being planted across considerable acreages; yet, muscadines remain a niche crop. We conclude that muscadines suffer from their short history of cultivation in a confined region and would benefit from breeding and marketing efforts to increase consumption, commercial acceptance, and awareness.
Selective leaf removal in the proximity of grape clusters is a useful practice to manage fruit diseases and otherwise improve fruit composition. The current recommendation in the eastern United States is to create a fruit zone with one to two leaf layers and to focus removal on the “morning sun” side of the canopy. We evaluated a more intense and an earlier application of fruit-zone leaf thinning relative to current recommendations to determine whether additional benefits could be obtained without a penalty of impaired berry pigmentation or other ill effects of abundant grape exposure. Fruit secondary metabolites and berry temperature were monitored in two different field experiments conducted with ‘Cabernet Sauvignon’ in the northern Shenandoah Valley American Viticultural Area (AVA) of Virginia. One experiment evaluated the effects of no leaf removal, prebloom removal of four basal leaves per shoot, and prebloom removal of eight basal leaves per shoot. The other experiment evaluated the effects of no leaf removal and postfruit set removal of six basal leaves per shoot. On average, exposed grapes heated to ≥30 °C for a 126% longer period (53 hours) than shaded grapes in the postveraison period (from color development through harvest). However, postveraison grape temperatures did not remain above provisional, critical temperature thresholds of either 30 or 35 °C for as long as they did in studies conducted in sunnier, more arid climates. There were minimal differences in berry temperature between east- and west-exposed grapes in the northeast/southwest-oriented rows of the experimental vineyard. Regardless of implementation stage, leaf removal consistently increased total grape phenolics measured spectrophotometrically, and either increased or had no impact on anthocyanins relative to no leaf removal. Grape phenolics and anthocyanins were unaffected by canopy side. Berry total phenolics were increased and anthocyanins were at least maintained in fruit zones void of leaf layers—a canopy attribute that reduces bunch rot in humid regions.
Fruit zone leaf removal is a vineyard management practice used to manage bunch rots, fruit composition, and crop yield. We were interested in evaluating fruit zone leaf removal effects on bunch rot, fruit composition, and crop yield in ‘Chardonnay’ grown in the U.S. state of Georgia. The experiment consisted of seven treatments: no leaf removal (NO); prebloom removal of four or six leaves (PB-4, PB-6), post–fruit set removal of four or six leaves (PFS-4, PFS-6), and prebloom removal of two or three leaves followed by post–fruit set removal of two or three leaves (PB-2/PFS-2, PB-3/PFS-3). Although leaf removal reduced botrytis bunch rot and sour rot compared with NO, effects were inconsistent across the two seasons. Fruit zone leaf removal treatments reduced titratable acidity (TA) and increased soluble solids compared with NO. PB-6 consistently reduced berry number per cluster, cluster weight, and thus crop yield relative to PFS-4. Our results show that post–fruit set fruit zone leaf removal to zero leaf layers aids in rot management, reduces TA, increases soluble solids, and maintains crop yield compared with no leaf removal. We therefore recommend post–fruit set leaf removal to zero leaf layers over no leaf removal if crops characterized by relatively greater soluble solids-to-TA ratio and reduced bunch rot are desirable for winemaking goals.
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