Trellising is the art of arranging the vine in space. The goals are to maximize light interception, minimize the number of additional inputs (e.g. labour,
material costs, maintenance, etc.), provide physical support and be compatible with the management situation, which includes machinery (see Fig. 6.12). In choosing a trellising system, factors such as product end use, harvest method, mechanization, cost and labour requirements have to be considered, along with the predicted vigour/capacity of the vines at that site.
Self- or stake-supported
The simplest training systems are staked vines or bush vines. The vine is trained to a short trunk tied to a stake on which a head with several short canes is left. Once the trunk can support the weight of the canopy and fruit on its own, the stake can be removed (see Fig. 6.13). Alternately, the stake can Fig. 6.11. Very vigorous vines in an Oregon, USA Scott-Henry-trained vineyard.
The upward-growing shoots are shading the adjacent rows as well as themselves;
the downward-trained shoots have been cut off by the mower. These vines are in desperate need of some good viticultural management!
Fig. 6.12. An example of where there is incompatibility between mechanization and trellis design. An entire section of row has fallen over due to mechanical harvester damage. Trellis designs for mechanized systems should be robust enough to withstand the additional stress they cause.
Fig. 6.13. Bush vines in a Californian vineyard. Note the tyre tracks indicating cross-cultivation and the wide vine spacings.
remain and canes can be trained upward and tied to the stake (see Fig. 6.14).
There are other forms of self-supporting systems, such as the basket vines, in which canes are woven together to form a low bowl shape, which may encourage the capture of dew, important in areas that cannot be irrigated (see Plate 27). Advantages of these types of systems are low capital cost, low vine densities suited to arid areas and the possibility of movement of machinery crossways through the vineyard. Disadvantages include low cropping capacity per hectare due to inefficient use of land area.
Single wire
Single wire trellising systems are used for a variety of purposes and are low cost relative to most other systems, due to only one wire being needed. Here, a single fruiting wire is used and shoots arising from the cane or spurs are free to grow in whichever direction they end up (see Fig. 6.15). In vine species with upright growth habits (most of the V. viniferaspecies), this creates a high hedge open at the bottom, whereas in those species with a trailing growth habit (e.g. V.
labrusca) the hedge form is lower and less open at the bottom. Though this system is not compatible with close row spacings, the canopy is usually quite open, leading to good fruit exposure, spray penetration and relatively high crop loads.
Fig. 6.14. Individually staked vines. Note the clean cultivated soil in this young vineyard.
The practice of minimal pruning can be combined nicely with a single- wire system. Vines are not pruned by hand, but rather trimmed by machine (see Fig. 6.16). The size of the cross-sectional box to which the vines are trimmed determines the approximate number of nodes left on the vine. Crop adjustment can be accomplished through trimming the vines after fruit set, when crop loads can be better estimated (usually, the bottom part of the vines is trimmed off in this operation), or later with a mechanical harvester (Pool, 1987; Fisher et al., 1997).
Hedge-type
Vertical Shoot Positioning (VSP, Fig. 6.17) is a widely used trellising system for the production of wine grapes and results in the box-shaped hedge that is seen in so many vineyard calendars. A fruiting wire is relatively close to the ground (typically 90 cm at a row spacing of 2.5⫺3.0 m), dormant canes wrapped to it (the horizontal cane version of this is called a Guyot system) and shoots are trained upwards from it during the growing season. This results in a fruiting zone above the cane, which localizes the crop relative to most of the canopy. Fruiting wires can number one or two, with one to four fruiting canes being typical.
Additional wires are needed to maintain the shoot growth in its vertical position, adding to the system’s cost. Labour is also required to position the Fig. 6.15. These grapevines are trained to a single wire trellis. The ones on the left side are mechanically pruned and the ones on the right spur pruned.
Fig. 6.16. A comparison of minimally pruned vines with hedge-type vines in the early part of the season. The minimally pruned vines have many more, but shorter, shoots than the hedge vines, which can lead to greater productivity due to greater capacity for photosynthesis.
Fig. 6.17. Wine grapes growing on a Vertical Shoot Positioned (VSP) trellis. Note the catchwires, made visible by the leaf removal in the fruiting zone, that are used to contain the shoots within the hedge-like shape.
shoots within the wire and keep them there, as vine growth habit and wind tend to make them fall out. Cultivars or clones with an upright growth habit are much better suited to VSP, as it is much easier to keep them within the wires. Typically, trimming of the sides and tops of the canopy is also necessary, as often VSP is used in areas where vigour is greater than the system can contain. To allow for more nodes to be laid down between vines, the canes can be arched rather than tied to the horizontal fruiting wire (see Plate 28), which also assists in levelling out shoot growth along the cane. Names of these variations are Pendelbogen, Umbrella Kniffen or simply Arched Cane.
Training to a Sylvoz system is a way of increasing the number of nodes left per metre of row without having to divide the canopy by a more expensive trellising option. Vines are cane or spur pruned to a mid-height fruiting wire, but additional canes are left trained downward and tied to a lower wire (see Plate 29). This spreads out the shoots and fruiting area ⫺the former being beneficial for canopy density, but the latter making it more difficult to target fruit sprays and perform effective leaf removal operations.
Divided canopies
Divided canopies were developed to address the concerns of maximizing crop and accommodating high vigour. The first significant breakthrough in this area was made by Nelson Shaulis and his research crew of the Geneva Experiment Station in New York, USA (Shaulis et al., 1967). The Geneva Double Curtain (GDC, Fig. 6.18) addressed the issues of increasing productivity (through better light interception per unit land area) and mechanization of ‘Concord’ grapes, which were primarily grown for juice production. The system is effectively two single wire systems set side by side. Due to the trailing growth habit of V. labrusca vines, two distinct curtains of shoots develop (though usually with the help of some shoot positioning). GDC has been adapted for use with other grapevine species, though its best application remains with trailing growth-habit cultivars.
Other horizontally divided canopy systems have been developed, such as the Lyre system, which is similar to the GDC in that it simulates two close- spaced rows of vines while only being a single row. The Lyre is so called due to the instrument-like arrangement of the two VSP-like trellising systems (see Fig. 6.19) when viewed end-on, which was chosen to optimize light interception and therefore productivity (Carbonneau and Casteran, 1987).
However, the capital costs of establishing this trellising system are high in comparison with that of most others, so the perceived benefits must be worth the additional expense.
A popular divided canopy system is the Scott-Henry (see Fig. 6.20) and its derivatives (e.g. Smart-Dyson) (Smart and Robinson, 1991). Rather than splitting canopies horizontally, this system splits them vertically, with one set of
Fig. 6.18. The view down the centre of a Geneva Double Curtain (GDC) trellis, showing cane-pruned vines and the distinct distance between the two fruiting wires.
Fig. 6.19. Looking down the inside of a row of vines trained to a Lyre trellis. It is an advantage if a person is able to walk down between the canopies and work on the shoots. In any case, there should not be any shoots bridging the interior of the two sides.
shoots trained upward and one downward. An advantage of this system is that it is easy and relatively inexpensive to retrofit to a VSP system, which is useful if the eventual vigour of the vines has been underestimated at planting.
Some generalizations on divided canopies would be that light penetration is increased through their use, which in part accounts for their beneficial effects on improving crop load and fruit composition. They also allow for more flexible matching of vines to potentially vigorous sites and stretch the yield:quality envelope. In many cases the cost of establishing or converting to a divided canopy system are justified given the benefits received over the life of the vineyard.
Other trellising systems
Overhead systems (e.g. pergola or parronal) are the most efficient in terms of land use in that almost 100% of the incident light is captured and used by the vines. This leads to high yields per unit area of land, but there is a cost in terms of trellis construction and difficulties in working with the system. A series of wires is strung between post supports and the vines trained along the top (see Plate 30), usually with a low number of vines per hectare compared with the previously mentioned trellising systems.
Fig. 6.20. Scott-Henry-trained vines in Mudgee, New South Wales, Australia. Of note is the distinct band of light running through the middle of the canopy, which demonstrates good practice with this system, as air should be able to move between the upper- and lower-trained shoots.
Overhead trellising is used in fresh, wine and raisin grape production, to varying extents. Adoption of this system in raisin production is growing as a result of techniques allowing raisins to be dried on the vine (DOV) rather than in between rows (Christensen, 2000).
Munson ‘T’-type trellises are used extensively for fresh grape production as well as for wine grapes and raisins. As its name suggests, a single post supports a horizontal brace on which three wires are strung up and down the rows.
Shoots are trained on the top of the trellis wires and the fruit hangs below (see Fig. 6.21). Variations of this have the top brace at an angle, where shoots are trained up and along it, allowing the fruit to hang underneath, but with better access for management and harvesting. In the case of the Swing-arm Trellis (Clingeleffer and May, 1981) the ‘T’ portion of the trellis also pivots, to improve vine mechanization and productivity.
There are many variations on these themes for providing a structure on which the grapevine can grow, each adapted to a particular situation or need.
For a review of these see Freeman et al. (1988) and Smart and Robinson (1991).
For those vineyards that are intended to be managed by hand, research such as that by Kato and Fathallah (2002) will be of increasing interest, as it has been demonstrated that certain types of trellising systems are more user- friendly than others, in terms of risk of musculo-skeletal disorders such as those associated with repetitive strain injuries.
Fig. 6.21. A ‘T’-type trellis, which encourages the fruit to hang freely under the canopy. This allows good access for sprays as well as for handling.
End assemblies
Trellises support much of the weight of grapevines and their fruit, as well as resisting movement caused by wind and vineyard machinery. The structures at the ends of the rows must resist the along-the-row tension caused by the weight on the trellis, as the intermediate posts carry the strain of the vines, fruit and even the accumulated weight of rainwater on them (Mollah, 1997).
The end assemblies must transfer the tension in the wire (which is, in large part, determined by the spacing between intermediate posts (Freeman et al., 1992)) to the ground and, as such, need to be more robust than the intermediate posts. The main load-bearing unit of an end assembly is called the strainer, and its ability to transfer the load to the soil depends on the trellis height, strainer diameter, leverage affected by its depth in the ground, and the soil itself (Smart and Robinson, 1991; Freeman et al., 1992; Mollah, 1997). Three main types of end assemblies will be discussed here that should be useful for most vineyard situations.
The tieback end assembly (see Fig. 6.22) is a system where the load is transferred though the end post to an anchor in the ground. The wire used to tie
Fig. 6.22. Tieback end assemblies. Note that two loops of wire are used to link the strainer to the end post and that the loops have a wire tensioner to adjust the strain on the posts.
the anchor to the end post should be equivalent in strength to the sum of all wires used in the row, where foliage wires count as half because they are not under as much tension (e.g. if there is one fruiting wire and four foliage wires, then the wire to the anchor should be equivalent to three wires) (Smart and Robinson, 1991). The tieback is cost efficient and allows for vines to grow unhindered right up to the last post of the row, but does require some additional headland for equipment turning compared with other systems.
A diagonal stay system (see Fig. 6.23) transfers the tension into the row using an angled brace, which can be made of wood or metal. The foot at the end of the diagonal component acts as a pivot for the strainer post, so that the tension attempts to twist the strainer up and over the diagonal stay. This is an effective system that is inherently stronger than a tieback one (Freeman et al., 1992, Mollah, 1997), and also requires less space outside the last vine in the row for headland. However, due to additional materials used, it does cost more, and there is some interference for vine training caused by the diagonal stay.
Fig. 6.23. Diagonal stay assemblies in a VSP vineyard.
The box end, or horizontal stay, assembly (see Fig. 6.24) is regarded as the strongest, as the design keeps the force on the strainer vertical rather than horizontal, distributing it over a larger area (Smart and Robinson, 1991).
Therefore, this post needs to be larger that the others. Though strong, the design is expensive to build and vines growing within the box are much harder to manage.
The failure of end assemblies is usually caused by either (i) insufficient strainer diameter or strength, leading to breakage (see Fig. 6.25); (ii) not
Fig. 6.24. Many rows of box end assemblies in a New Zealand vineyard. Note how constrained the growth of vines is inside the box compared with those in the row.
Fig. 6.25. A free-standing end assembly that has failed due to inadequate strength.
The adjacent row has already been retro-fitted with a diagonal stay assembly in recognition of the original oversight.
putting the strainers into the ground far enough, which leads to them being pulled out; or (iii) soil not being strong enough to bear the load, which leads to strainers tilting or moving through the soil (see Fig. 6.26). A thorough analysis of predicted trellis loading and soil strength, before determining the type of end assembly to use, will prevent costly repairs and lost crop in the future.