Pruning and Training Grapevines
Mechanical Pruning
Many winegrape cultural practices, including pruning, canopy management, and harvest, are labor-intensive and time-sensitive. In addition, California and many other winegrape-producing regions are facing rising labor costs and labor shortages. Thus, the adoption of mechanical winter pruning in vineyards has been growing worldwide to reduce the labor required for traditional, time-consuming manual operations. Hand pruning accounts for up to 75 percent of the yearly labor demand, and such high labor costs can be reduced by 50 to 90 percent through mechanization, depending on the training system used and the extent of hand clean-up.
Vineyard Design Considerations
Factors to consider when designing a vineyard for mechanization include available equipment, adequate inter- and in-row spacing, headland size, trellising, irrigation, and cultivar selection. Long, straight rows that are adequately spaced are essential. Long rows increase operating efficiency, while straight rows minimize vine injury and damage to line posts. Adequate interrow spacing is desired to allow for lateral adjustment of equipment during operations. Row spacing in mechanized vineyards should be 9 to 11 ft (2.7–3.4m) for single-canopy systems and 14 to 31 ft (4.3–9.7m) for double-canopy, vertically divided systems. In manually tended vineyards, headland widths of 25 ft to 30 ft (7.6–9.2m) have been adequate.
Mechanical Box Pruning
Mechanical box pruning is a mechanized pruning method in which the vine canopy is trimmed into a “box” or rectangular shape during the dormant season using a combination of horizontal and vertical cutting bars mounted on a tractor or self-propelled frame. It is called “box” pruning because the machine cuts along the top and sides of the vine canopy, effectively “boxing” it in and leaving behind a uniform spur framework.
Mechanical Pruners
Commercial vineyards commonly use tractor-mounted mechanical pruners, also called pre-pruners, for initial cuts on dormant vines. These large machines drastically reduce labor requirements across a whole vineyard, but still require follow-up hand pruning for precision.
Hedger Bar Pruners
Hedger bar pruners, when mounted singly, have a single plane of cut and low penetration into the dormant canopy. They have an efficient cutting mechanism consisting of two opposing serrated cutting surfaces that operate in opposite directions along the plane of travel, matching the tractor’s ground speed.
Rotary and Drum Pruners
Rotary and drum pruners, whether mounted singly or in stacks, have greater penetration into the dormant canopy than do hedger bars (Figure 9.5). Depending on the cutting surface used (rotating drums or saws), they can be used either for summer pruning or for setting the height of the bearing spurs during dormant pruning.
Effects on Yield and Fruit Composition
Pruning is a rough regulator of yield because of the unpredictable nature of fruit buds breaking from nonproductive positions. Therefore, other techniques are needed to control yield. Generally, mechanically pruned vineyards are higher yielding than manually pruned vineyards by approximately 30 percent in the initial eight years. However, as the vineyard balances and the fruit zone becomes less fruitful because of mutual shading, the yield levels off, and there are negligible differences between manually and mechanically pruned vineyards.
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