The function of a trellis system is to support the vine to achieve an optimum production that is dependent on the capacity (productivity) and vigour (rate of growth) of the vine.
The capacity of a vine is generally linked to the type of soil and the variety and rootstock used. A low vigorous site requires a simple trellis system along with higher plant density. A high vigour site may require a more complex trellis system and lower plant density in order to manage the vigour produced by the vine.
Trellis designs vary from low vertical shoot positioning (VSP) to the high overhead T-bar system such as Geneva Double Curtain (GDC). When deciding on the height of the trellis system, some consideration should be given to the following points:
The optimal fruiting wire height is generally 0.9-1.2 m. This is comfortable for workers, allows good air drainage and is adaptable to mechanical harvesting.
The choice of a training system is determined by a vine’s growth habit, vigour, fruitfulness of its base buds, soil type, soil fertility, site selection and economics of harvesting. Most vinifera are more upright in their growth habit, so a low renewal zone is best. If mechanized pruning is contemplated, only certain training systems are appropriate.
A good training system:
Training systems for vinifera must take into consideration their upright growth habit, relatively winter-tender trunks and close vine and row spacing. These features require systems that minimize permanent wood, use double trunks, keep renewal zones close to the ground (0.9-1.2 m) and provide trellising to control and contain shoot growth.
These criteria are met by training systems that keep the cropping area close to the ground, such as the pendelbogen system (European Loop) and VSP and vertically divided canopy systems such as the Scott Henry System or modifications of this system. Trellising to systems with high trunks, such as the GDC, are justified if vine vigour is very high and the risk of winterkill of trunks is very low.
Image credit: Dr Pat Bowen and Carl Bogdanoff (AAFC PARC Summerland, B.C.)
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Vertical systems consist of a single fruiting wire located at about 1 m above ground plus several catch wires, which are paired opposite each other or single on one side of the post or alternate on opposite sides, and are either permanently attached or movable paired wires.
Spacing of the catch wires depends on the variety and environment. Windy locations should have the first foliage wire at 20 cm above the fruiting wire, on the lee side of the wind, with other foliage wires spaced at 30 cm from there on.
Hooks or slanted nails should be used to hold movable wires in place. Permanent single wires should be attached on the wind side of the posts so that they are pushed against the post rather than pulled away from it by the wind.
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Developed in Oregon, this system consists of two fruiting wires, one at 96 cm on one side of the post and the second at 126 cm on the other side of the post, with 30 cm separating the two wires. This was originally a cane pruned system.
The shoots on the upper wire are trained upwards between the foliage wires, and the bottom shoots are turned downwards. Separation of the two fruiting areas should begin before bloom with placement of the foliage wire outside the bottom fruiting wire shoots. During bloom, these shoots are turned downward.
The wide space between the two fruiting wires is needed to permit good air circulation and light penetration. This window should be kept open at all times.
The Scott Henry system can be modified by placing the fruiting canes of one plant on the lower fruiting wire and the next plant on the higher fruiting wire, avoiding the competition of upper and lower wires when one vine is used to produce canes for both fruiting wires. This will also help prevent one level from being dominant over the other.
Other modifications consist of placing one cane on the higher fruiting wire and developing this into a cordon with spurs alternating into an upper and lower direction.
This system uses a single cordon with half the shoots allowed to be trained downward and half trained upward. Each shoot position is alternately trained up and down. This has the advantage of decreasing the canopy density thus allowing good spray penetration and keeping yields at a high level.
The labour costs of this system are higher than that of the Scott Henry or VSP systems.
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There is no positive response to any divided canopy training system by vines that have a low canopy density (less than 0.7 kg cane prunings per metre of row), but there is a major response when divided canopy training is used with vines of high density canopy (more than 0.7 kg prunings per metre of row).
The major response is the illumination of the renewal areas of the canes or spurs and all the benefits that this brings. To obtain the full benefit of this response, shoots must be positioned to permit sunlight to reach the renewal areas. A divided canopy with shoot positioning:
The heart of the divided canopy training system is the shoot and leaf exposure to light. Without shoot positioning, the structure of a divided canopy training system is meaningless.
Shoot positioning takes time — usually 80 hours of work per hectare. Divided canopy systems should not be attempted unless you are willing to do shoot positioning. Shoot positioning should be done twice: the first time early in the four-week period after bloom and the second time in 2-3 weeks as the shoots again try to become horizontal.
The Geneva Double Curtain trellis was originally designed for Concord grapes, but now it is also used for French hybrids and vinifera varieties. The GDC system has fruiting wires 1.2 m apart and 1.8 m above the ground. The system usually has two cordons of 1.8-2.4 m long, trained alternatively to the right and left cordon wires.
Spur pruning is used. Downward pointing spurs direct growth away from the centre of the trellis and not into the ally where tractors work. Vinifera varieties generally (but not always) have upright growth habits, requiring the use of a movable foliage wire to downward shoot positioning devigorates the shoots and promotes good basal node exposure. Sometimes fruit is sunburned when it is overexposed.
The GDC system requires the maintenance of two distinct curtains of leaves. This is done through shoot positioning, a process of combing outward and downward all the upright-growing shoots and those growing into the centre of the canopy. This is best done after bloom and again 10 days to two weeks later. The centre of the vine is opened up to sunlight, and maximum leaf and fruit exposure is maintained.
Similar in structure to the GDC, the wide T trellis system has two horizontal wires 0.9-1.2 m separation. It is traditionally not shoot positioned, but leafwork must be done to keep the canopy open and allow basal buds and fruit exposure.
The advantage is greater yield per plant with good sun exposure. The disadvantage is the difficulty in working with the height of the canopy and that it is not conducive to mechanical harvesting. Unless rows are very wide, the growth causes problems with tractor movement.
The vine trellis is a structure that has to support large loads. The vertical load includes the weight of the fruit, vine and wire. The lateral load is composed of wind forces and machinery errors. Longitudinal load consists of the tension placed on the wire to prevent the trellis from sagging.
The fruiting wire is expected to take the most stress and should be at least 12 gauge galvanized high tensile wire. The training or support wires should be 13 or 14 gauge galvanized high tensile wire.
Posts are normally sharpened, treated wood posts that are 2.4-2.7 m (8-9 feet) long. They are long lived (20 years) and very strong and flexible. The use of 7.6-10 cm (3-4 inch) posts for in-row support and 10-15 cm (4-6 inch) posts for end posts is common practice.
Metal posts may also be used and can be air vibrated into the soil, but they do not have the strength or flexibility of the wooden posts and are more expensive.
There are many systems in use to offer the strength for tensioning the trellis wire. A few examples include:
There are a number of different steel anchors on the market, which are either buried or screwed into the ground and attached to the end post. These perform very well if properly installed.
It is important that the anchor chosen will be suitable for the type of soil it is going into. Some anchors that are screwed or spun into the ground perform very well on sand or loam soils that have very few rocks. For rocky ground, there is a special expanding type of anchor available, which works well. There are also anchors that can be drilled into the ground that are suitable for rocky soil.
Longer rows and heavier crops need better anchor systems!
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