Effect of Pruning Severity on 'Carlos' Muscadine Grape (Vitis rotundifolia) Yield, Quality, and Disease Incidence
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Date
2007-12-11
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Abstract
Interest in horticultural crops such as the muscadine grape (Vitis rotundifolia Michx.) has grown in recent years due to declining production of tobacco and other agronomic crops. Most growers choose to mechanically prune muscadines due to the low returns on wine grapes and the high cost of labor. However, such pruning practices may reduce long-term vine vigor and juice quality. The objective of this study was to quantify how different pruning levels affect vine vigor, fruit quality, and disease incidence on 'Carlos' muscadine grapes. Four pruning levels were established on four-year-old vines: the retention of either 200, 300, or 400 nodes⁄vine or simulated mechanical pruning (SMP). The treatments were applied in winter 2006 and 2007 at three North Carolina vineyards, one each in Duplin, Scotland, and Orange counties. It must be noted, a freeze occurred in early April 2007 that caused severe damage on grapevines across the state including vineyards used in this study.
Although SMP vines had more than double the number of original nodes, the 300 and 400 node treatment vines produced yields similar to SMP vines in different years at different locations. Severe pruning and cold injury to buds forced latent secondary and tertiary buds to break that may have supplemented the muscadine crop. In a study in 2007, shoot origin (e.g. base bud versus count bud) did not affect shoot fruitfulness. Base buds were less mature at harvest than count buds, presumably as a result of delayed budbreak. Fruit from SMP vines did not differ in juice quality parameters (percent soluble solids, pH, or titratable acidity) in either year from other pruning treatments.
The Ravaz index, a ratio of fruit yield (kg) to pruning weight (kg), indicates the balance between fruit yield and vegetative growth. Typical values of balanced V. vinifera grapevines fall between 5.0 and 10.0. Indices in the present study ranged from 2.3 to 12.7 depending on treatment, location, and year. The SMP vines in the Duplin County vineyard (5.7) and the 400 node treatment vines at the Scotland County vineyard (5.8) had values that fell within the desired range. Indices from 2007, reflect the freeze-related yield reductions and excessive vegetative growth. Therefore, they are not representative of a normal production year.
The point-quadrant technique was used to quantify the muscadine canopy in 2006. SMP vines showed a significant advantage in canopy fill over selectively pruned vines in the spring of 2006 at the Orange County vineyard. The technique used in the present study was based on use for V. vinifera vines. Due to the different growth habit of muscadines, the technique as used in the present study did not adequately characterize the distribution of the canopy or fruit and may need to be modified.
Shoots tended to be longer at the head of the vine compared with those at the ends of the cordon in both years and in all three measurements times. A gradient in maturity, from green at the vine head to overripe at the distal ends was observed in 2007 and may have resulted from shading at the vine head. In 2007, the shoots in the middle area of the cordon produced fruit of optimum maturity at harvest and also tended to be more fruitful.
At this time, it is not possible to state whether hand-pruning may be an economical option for growers producing grapes for processing due to the Easter freeze in 2007. However, based on results in 2007, the SMP treatment provided the highest yield with negligible differences in vine vigor, juice quality, and disease incidence.
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base bud, selective pruning, transects, mechanical pruning, canopy, shoot length, freeze, cold injury, count bud, Ravaz index
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Degree
MS
Discipline
Horticultural Science
