Chapter 10

Vineyard Canopy Management

Techniques for Vineyard Canopy Management

Very few grapevine canopies fall within the preferred range of the parameters that characterize the ideal canopy. In areas with deeper, often somewhat fertile soils, normally abundant rainfall, and a long growing season, these factors combined with the vine’s natural vigor, may lead to very vigorous vines, often with very dense canopies. Excessive fertilization and/or over irrigating may also result in excessively dense canopies. When this is the case, canopy management techniques such as shoot positioning, shoot thinning, hedging, leaf removal, and cluster thinning may help in opening-up the canopy to expose the fruiting and renewal zones of the canopy to better illumination and air movement. These practices can have a significant impact on fruit quality and vine productivity both in the year they are applied and in subsequent years. If the canopy is naturally dense year after year, it may require changes in the trellis system to alleviate some of the crowding.

Shoot Positioning

Shoot positioning is another important element of canopy management in the vineyard. Proper shoot positioning results in orienting shoots to create a uniform distribution of foliage that minimizes shading of fruit. An added benefit of shoot positioning is that it makes other canopy management chores, such as hedging and leaf removal, easier to accomplish. It also improves the efficiency of operations such as pruning. Not only is shoot positioning important for the current growing season, it also has an impact on productivity by encouraging the development of more fruitful buds for next year's crop.

Timing of Shoot Positioning

The best time to position shoots is one to two weeks’ post-bloom, when most shoots can be positioned without breakage and before their tendrils have secured the shoots to wires or other supports. On low-cordon bilateral systems, it is easier to do if the foliage catch wires are not in fixed positions but are movable and placed below the cordon level after winter pruning.

Shoot Thinning

While dormant pruning is used as the primary tool by grape growers to maintain vine structure, canopy architecture and regulate crop level, shoot thinning provides an additional canopy management tool to bring vines into vegetative and fruiting balance by reducing shoot density and the number of clusters per vine. The objectives of shoot thinning include: (1) to attain a favorable ratio or balance between fruit and foliage; (2) to promote light and air penetration into the fruit zone; (3) to encourage uniformity in shoot and crop development along the length of a cordon or cane; (4) to minimize the risk of diseases; (5) to improve quicker drying of leaves and fruit, as well as increases spray penetration; and (6) to facilitate vineyard operations and control costs.

Timing of Shoot Thinning

Shoot thinning should be done early in the growing season, when shoots are approximately five to six inches long, since they are easier to remove, and not more than 10 to 12 inches (25 to 30 cm) long. Shoot thinning should be timed after the date of last “expected” frost, such that secondary or non-damaged primary shoots can be retained in the event of a late spring frost.

Shoot Selection

Shoots from the base of spurs, multiple shoots from the same node, shoots growing from non-spur positions or originating in the head region or on the trunk are all candidates for removal, unless needed to replace an old or poorly positioned spur or an old cordon. Usually, all sterile (unfruitful) shoots are removed during thinning.

Shoot Density Recommendations

A shoot density of about three to six shoots per linear foot of cordon normally achieves the benefits stated above for vinifera cultivars. This frequently corresponds to removal of all shoots except those originating from count buds on spurs.

Impacts on Fruit Quality

For vinifera cultivars shoot thinning has been shown to result in higher Brix and pH in fruit and sometimes results in an increase in berry skin phenolics and anthocyanins. These effects are likely due to a combination of managed crop levels and increased sunlight exposure of the canopy and fruit.

Mechanized Shoot Thinning

Cordon brushes (See Figure 10.1) are used in the removal of unwanted shoots from cordon-trained vines. They are most commonly used to remove shoots below the cordon, in place of hand suckering, but can also be run a bit higher into the fruiting zone to remove a few cluster bearing shoots, if lower crop yields are desired.

Hedging

The goal hedging is to remove excess primary and lateral shoot growth from the top and sides of the canopy. This is needed to prevent shading and entanglement of shoots between vine rows and to allow worker and tractor traffic through the vineyard. Although hedging decreases canopy by cutting primary and lateral shoots, it does not directly decrease the vine's inherent vigor and can further promote growth by inducing lateral shoot growth in vigorous vines when conducted in early to midsummer.

Timing of Hedging

Hedging is usually conducted from fruit set to véraison and is important to maintain adequate light exposure of leaves, fruit, and developing buds in dense canopies that have excessive vegetative growth. Hedging too early in the growing season should be avoided as it can initiate lateral growth and increase canopy density.

Impacts on Fruit Quality

As with shoot thinning, hedging shows variable impacts on fruit quality, including a potential alteration of yield, Brix, pH, and titratable acidity.

Leaf Removal

Leaf removal is typically conducted in and around the cluster zone to allow varying levels of sunlight exposure and airflow. The objective leaf removal is to have an average of one to two leaf layers remaining in the fruit zone after the leaves have been pulled. The goal is not to completely strip all the foliage from around the fruiting zone, but to provide between 40 and 60 percent exposure of the clusters (Allen, 2011). An adequate number of leaves must remain on the shoot to produce carbohydrates to support vine growth, fruit development and ripening, develop overwintering reserves and to allow vine shoot and bud winter hardiness. This can be accomplished by removing a relatively small number of leaves from the vine in the area around the fruit clusters, usually. Restrict leaf removal to those leaves positioned at or below the cluster on the shoot since those above the shoot are the primary source of carbohydrates for the developing cluster (Cantacuzene, 2007).

Timing of Leaf Removal

This practice can be done any time after fruit set and before véraison, but is best done by the time the individual berries are pea-sized, usually about 2 weeks after fruit set. Removing leaves at fruit set allows the fruit to acclimate to a certain amount of sun exposure and promotes bud fruitfulness for next year’s crop (Cantacuzene, 2007). More traditional leaf-removal programs promote leafing at fruit set.

Impacts on Fruit Quality

By directly reducing the leaf layer number in the fruiting zone, leaf removal creates a much more favorable microclimate within the canopy enhancing the quality of the fruit.

Vineyard Deleafing Machines

Traditionally, leaves are removed by hand, but due to the high cost and low availability of hand labor, more vineyard managers are using deleafing machines to do this work. All these machines need access to the fruit zone. Mechanized leaf removal is more efficient with training systems such as VSP (vertical shoot positioning) because the fruit is placed uniformly along the cordon than with systems that have fruit scattered around the canopy such as Geneva Double Curtain trellis system.

Cluster Thinning

Cluster thinning is a practice used to adjust fruit yields to obtain balance between fruit and canopy to achieve optimum ripeness (See Figure 10.4). Crop thinning can be used to remove undersized, poorly set or immature clusters. It can also be used to reduce bunch rot in tightclustered varieties like Chenin blanc too.

Timing of Cluster Thinning

Cluster thinning can be done at any time from pre-bloom through just prior to harvest. Timing is important because shoots and flowers (or fruit) are competing with each other for resources within the vine, and, depending on when thinning is reduced, there may be different results for either the canopy or the fruit. Research suggests that pre-bloom thinning can lead to increased fruit set of the remaining clusters and can potentially increase vegetative growth. In small or weak vines, removing crop earlier in the season may help improve berry development because there is less competition, allowing for more vegetative growth to support the berries through ripening.

Impacts on Fruit Quality

Crop thinning, when warranted, can help ensure that the fruit obtains adequate ripeness (Brix, pH, and titratable acidity).

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