Fig. 6.33. Examples of cultivated (upper) and packed (lower) soils used to assess their effect on fruiting cane temperatures during frost events (from Creasy, 2004).
The influence of frost cloth tents over the canes was also evaluated, but was found to make little difference. Note how dark the moist soil is, contributing to the amount of energy that can be absorbed during the daytime.
are being grown. In terms of achieving the optimum exposure, site selection is still the first step. Selecting an appropriate site has a life-of-the-vineyard impact, so choosing one that is compatible with the production goals is important. For example, planting a vineyard on a particularly vigorous site will result in much additional time and labour spent correcting the excess vigour, which shades the fruit, through shoot trimming, shoot thinning, leaf removal, etc.
The next important opportunity to affect your canopy management is through scion and rootstock choice: both should be matched to the site (or vice versa) and its potential for vine growth, e.g. choosing a shallow-rooting rootstock for a deep fertile soil to minimize the vigour effect.
Vine planting density is also an important pre-planting decision that affects canopy management. Spacing that is too wide can result in vines that cannot sustain enough growth to fill the trellis. Spacing that is too close can result in vigorous growth and crowded canopies. If there is potential for very vigorous growth, a divided canopy should be considered right from the start.
Row orientation is also important. North⫺south-oriented rows have east- and west-facing sides and therefore the sun will spend half the day shining directly on one side and half the day shining on the other. East⫺west-oriented rows have a north and a south side to the canopy, but only the north side receives direct sunlight. Fruit from the continually shaded south side of canopies ripens more slowly and may be more susceptible to disease than the other side, because of the lack of sunlight (Naylor et al., 2003). Therefore, fruit from E⫺W-oriented rows tends to be less uniform.
Cover crop, irrigation and fertilization can be management tools that influence the vegetative growth of the vine. Vines will grow best in a vineyard with luxurious levels of water and fertilizer, and with bare soils. Thus the canopy management goal is to manage canopies to fit within the trellis, using any management tool available.
Leaf petiole analyses can be used to monitor the nutritional health of the vines, and soil nutrient tests can supplement this information. This information should be used to apply to the vines only those nutrients that are needed.
Limiting the amount of water accessible to the vines is an effective way of reducing vegetative growth. This can be either directly, by managing irrigation inputs, or indirectly, by managing between-row cover crops. Monitoring and maintaining soil moisture levels to appropriate levels for desired vine growth is essential in minimizing the number of canopy management interventions that are needed.
Shoot thinning
In terms of active, in-season, canopy management, shoot thinning is an effective tool for reducing canopy density. If a vine has been pruned to two-node spurs, non-count shoots may still arise even if the vine is pruned to approximately the
right number of nodes to achieve balance. These non-count shoots generally are not fruitful, increase canopy density and should be thinned out.
Shoot thinning is especially important in the head area of the vine, as there are many latent buds embedded in the wood that can develop into non-count shoots, crowding the renewal area.
The best time to perform shoot thinning is early in the season, when the shoots are about 15 cm long ⫺they are easy to see and come off easily at this stage. Later in the season the base of the shoot becomes more firmly attached to the cane or spur and the shoot must be cut off. More non-count shoots can grow as the season progresses, but management of cover crops, irrigation or other techniques could be used to decrease vine vigour and prevent this. The effect of shoot thinning alone as a canopy management device can be significant (see Fig. 6.34).
Fig. 6.34. Shoot thinning can have a positive impact on vine canopy density.
An unthinned ‘Pinot meunier’ canopy (upper) shows little light coming through from the other side. The shoot-thinned canopy (lower) demonstrates a much more open canopy.
Shoot thinning, in the ideal scenario, is a temporary fix to problems with the canopy. If shoot thinning is necessary every year the vines may be out of balance, and making a more permanent change to bring the vines into balance would be prudent (e.g. a trellising change, removing or planting more vines, changing the cover crop, etc.).
Shoot positioning
Another vital aspect of canopy management for most trellising systems is shoot positioning, which must be practised diligently to get the best out of them. Often, what is desired is a range of shoots positioned perpendicularly to the fruiting wire, either straight up (e.g. for VSP) or straight down (e.g for half the canopy of a Scott-Henry trellis or for Geneva Double Curtain). Shoots growing out into the row, down and below the fruiting wire (for upright trellises like VSP) and also, very importantly, shoots growing along the row, should be repositioned as early as possible since these contribute to shading and also tend to develop strong lateral growth (see Fig. 6.35). The out-of-line shoots have implications for the effectiveness of shoot topping, as described below.
Fig. 6.35. Shoots in a VSP that are not vertical. These horizontal shoots are the source of many leaves in the fruiting zone, which leads to high canopy density, fruit shading, poor spray penetration and thus increased risk of disease.
Foliage wires are an important part of many trellising systems. If these wires are lowered at pruning time, in the spring, when the shoots reach 25 cm or so in height, the wires can be lifted into place to guide and support the developing shoots. Additional wires can be lifted up to support further growth, and wires can also be shifted up the trellis as needed. This lessens the amount of hand-tucking that is required. Note that, in areas with high winds, catch wires also help prevent shoot breakage.
Shoot topping and hedging
Shoot topping (summer pruning or hedging) is another temporary-fix manage- ment tool. As long as growing conditions persist, the vine will continue to grow:
under ideal conditions a shoot can grow to many metres long in a single season.
This would be enough to grow up and out of the top of a typical trellis and back down to trail on the ground. Clearly, such long shoots would limit access through the vineyard as well as go against the goal of optimizing exposure of the maximum percentage of leaves and fruit.
With a well-balanced vine, shoot growth will slow as the vines approach fruit set and stop by the time the fruit is pea-sized. Shoot length at this point wouldn’t be far outside a typical trellis and shading would not occur. However, in most vineyards vines are able to grow much more than this and, to prevent shading between and within the rows, any parts of the shoots growing outside the trellis volume should be cut off (see Fig. 6.36).
It is important not to cut the shoots too short, however, as typically there must be ten to 14 leaves on each shoot to support the development of a typical crop load and the rest of the vine (Howell, 2001). Most trellis designs should accommodate a sufficient amount of shoot.
There is the possibility of lateral growth after initial topping. Lateral shoots will tend to develop from the shoots after topping, so their development should be monitored to determine when to top again. Regrowth should not extend outside the trellis volume to the point where it begins to shade other parts of the vine. In some vineyards shoot topping may need to be performed many times in a season ⫺an expensive proposition.
Leaf removal
There are a number of reasons for leaf removal on vines. One follows along from the primary goal of canopy management: to optimize the exposure of fruit to the sun. In general, this hastens fruit maturity, increasing soluble solids and decreasing titratable acidity (TA), and results in increased varietal aroma, flavour and colour (Smart and Robinson, 1991).
The amount of leaves to be removed varies with the desired end use of the grapes. For wine grapes 60% or more exposure of the clusters to the sun is regarded as the most beneficial (Smart and Robinson, 1991). In some vineyards, 100% leaf removal in the fruiting zone is practised (see Plate 36), though this can result in sun/exposure damage to some of the fruit (Kliewer and Lider, 1968). Optimum leaf removal opens up the canopy around the fruit sufficiently to obtain the benefits described, but not so much that direct sun can harm the fruit. For some production regions or end uses, less direct exposure to the sun may be warranted as grape flavours may be changed too much.
One major outcome of leaf removal is a reduction in the incidence of botrytis infections (Gubler et al., 1987). For this, it is often necessary only to remove leaves from just the east side of a N⫺S-oriented row. This exposes the fruit to the morning sun, which will help to dry out the area sooner, reducing the number of infection periods. On an E⫺W-oriented row, it is usually best to remove leaves on the side of the canopy facing away from the sun to improve light exposure. If the canopy is wide or thick, leaves from both sides may need to be removed to obtain a sufficient improvement in airflow and exposure.
The best time to remove leaves depends on the situation, but it should not be performed prior to fruit set, or crop load and flower cluster initiation may be affected (Poni et al., 2005). Earlier leaf removal ensures that the berries develop Fig. 6.36. Trimming shoot tops and sides with a mechanical hedger, which maintains the canopy in the shape necessary to prevent between- and within-row shading.
in an open environment, which is beneficial as if it is left too late (e.g. until after véraison), berries may be burned through this sudden exposure to the sun (see Plate 37).
Other methods
Most active management of vines concerns manipulation of the fruit, shoots and leaves. However, aside from the use of cover crops and control over irrigation, the roots can also be managed through pruning. Much as the pruning of canes limits vine capacity, because there is a balance between root, shoot and fruit growth, if the roots are also pruned there can be a decrease in shoot growth. In practice this is accomplished by running a strong tine through the soil down the vineyard row, breaking vine roots that are growing out towards adjacent rows (see Fig. 6.37). Ripping can be carried out intensively (two sides of each row), or less so by ripping every other row.
Fig. 6.37. Root ripping, or the breaking of roots that are growing out between the rows. This practice prunes growth below ground in much the same way that canes are pruned above ground, and also limits the capacity of the vines.
Things to avoid
1. Wide canopies: a thick canopy presents difficulties in two ways. One, it is difficult to manage a thick canopy. Exercises such as leaf removal are difficult to perform as interior leaves need to be targeted and it may require more time to remove enough leaves if the canopy is wide. Two, it presents problems in disease control as a thick canopy decreases light reaching inside, reduces air movement, increases relative humidity within the canopy and decreases spray penetration.
All of these can contribute to the increased risk of disease (Thomas et al., 1988).
Additionally, more fruit will be within the canopy where it won’t be well exposed to light, and it won’t mature as quickly or accumulate as much colour.
2. Dense canopies: for reasons of exposure and disease incidence already mentioned, a dense canopy works against the goal of a high-quality crop (see Plate 38). Dense and shaded canopies also reduce bud fruitfulness the following year, resulting in smaller potential crops and a tendency for the vine to move to a vegetative cycle (Smart and Robinson, 1991). Use shoot thinning and leaf removal as temporary measures, and investigate ways of reducing vegetative growth in a more permanent way.
3. High shoot densities: a contributor to dense canopies, this commonly occurs due to over-pruning (and thus the development of many non-count shoots) or leaving too many canes on fruiting wires. This may be an indication that dividing the canopy may be a better management option. Alternatively, you may be able to change your irrigation scheduling or use of cover crops to reduce the amount of water available to the vine.
4. Large gaps in the canopy: areas of the trellis not filled with canopy are effectively wasted. Gaps can be caused through missing vines or inadequate growth. Replant any missing vines, especially early in vineyard development. If the vines cannot maintain adequate growth to the fill the canopy (both along the row and up to the top of the trellis), then ensure that the vines are healthy, receiving enough water and nutrients, etc. If nothing is amiss, then the vine spacing may have been too wide, and adjustments to other management practices ⫺such as removing/changing cover crop, irrigation and fertilization plans, etc. ⫺should be made to increase vine capacity.
Quantifying change in the canopy
There are many reasons why the ability to acquire hard data on canopy characteristics, such as density and fruit exposure, would be useful: (i) in testing the effectiveness of shoot thinning on reducing canopy density; (ii) in monitoring changes in irrigation management on shoot growth and fruit exposure; and (iii) in performing quality control on contracted vineyard labourers, etc. In each case having some figures to back up personal observations is helpful.
The Point Quadrat method of evaluating vertical canopies is one such tool (Smart, 1988). In this a thin rod, simulating a ray of light, is pushed through the canopy at fruiting zone height. Each intersection with a leaf or cluster is recorded, and the process repeated at intervals of 20 cm down the row. If the rod makes no contact with anything, then the record for that point is considered a canopy gap. This simple, if somewhat tedious, operation can yield useful data about canopy characteristics, such as (i) leaf layer number (LLN, the total number of interceptions with leaves over the total number of insertions); (ii) interior leaves (the total number of leaves surrounded by either a leaf or a cluster over the total number of leaves); (iii) interior clusters (ditto, but for clusters); and (iv) percentage canopy gaps (the total number of gaps over the total number of insertions).
The Point Quadrat data align nicely with other means of measuring canopy density, including the use of light meters (Smart, 1988). This system’s advantages are (i) only basic equipment is needed; (ii) it is objective; (iii) it is not difficult to train people to collect the data; and (iv) it gives useful information.
The major disadvantage is that is requires quite a bit of time to collect the data.
However, in those instances where differences in canopies need to be quantified, the Point Quadrat method is worth serious consideration.
More recent methods of evaluating canopy density include (i) the optical recognition of canopy gaps ⫺usually using a digital camera in the visible or infrared range to detect areas of the canopy through which light can pass (known as the gap fraction, Dobrowski et al., 2002); and (ii) the amount of green within the canopy zone. It is to be expected that there will be advances in this area, which will allow the routine collection of data on canopy status in a vineyard, even as the season progresses.
The results of good canopy management are;
1. An open canopy.
2. A uniform canopy, which is an easy-to-manage canopy and one that can produce a higher quality of fruit.
3. Less disease: powdery mildew development is inhibited by sunlight (Willocquet et al., 1996), and botrytis and other diseases need moisture and high humidity for optimal development (Thomas et al., 1988), and thus opening up the canopy decreases the length of time when conditions are favourable for disease organisms as well as improving spray penetration.
4. Higher yield: better shoot exposure means less loss to disease, greater fruitfulness and a greater ability to ripen a crop.
5. Higher-quality fruit: not only can there be more fruit, but it can all be of better quality: with good canopy management, there will be an increase in percentage soluble solids, colour, fruit aromas and flavours and decreases in TA and herbaceous aromas and flavours (Smart et al., 1988).
6. A higher-quality end product.