Trellis Systems

The function of a trellis system is to support the vine to achieve an optimum production that is dependent on the capacity (productivity) and vigor (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 vigor site may require a more complex trellis system and lower plant density in order to manage the vigour produced by the vine.

Trellis Design

Trellis designs vary from low vertical shoot posi-tioning (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:

  • in many cases the lower the fruiting wire to the ground the lower the acid level of the harvested fruit
  • in areas of frost risk the lower fruiting wire increases the risk of damage by frost as well as inhibiting air flow
  • hand harvesting and pruning become back breaking chores with both the very high trellis and the very low trellis

The optimal fruiting wire height is suggested to be between 90cm-1.2meters. 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 con-templated, only certain training systems are appropriate.

A good training system:

  1. spreads canes on a trellis to allow movement of equipment through the vineyard;
  2. arranges trunks and canes to avoid competi-tion between vines;
  3. provides a renewal zone for pruning that keeps the vine form and yield;
  4. minimizes shoot crowding, leaf and fruit shading leading to high fruit quality, good disease control, and steady yields;
  5. places the fruit in a position to allow ease of harvest, adequate spray penetration, and ex-posure to sunlight;
  6. develops a continuous area of foliage with well exposed leaves;
  7. encourages uniform and high bud break.
  8. maximizes leaf and nodes to be retained at pruning to maximum sun exposure.

Training Systems

Training systems for vinifera must take into consideration the 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 (c. 90cm-1.2m), and provide trellising to control and contain shoot growth. These criteria are met by training systems which keep the cropping area close to the ground: e.g. the pendelbogen system (European Loop), 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 vig-our is very high and the risk of winterkill of trunks is very low. Below is a list of the most common types of trellis systems and pruning practices used in the Okanagan and Similkameen Valleys.

Table 3.3 Percentages of Production Practices used in the Okanagan and Similkameen Valleys

Figure 3.3 Vertical Shoot Position System

 

Vertical Shoot Positioned Canopy

Vertical systems consist of a single fruiting wire located at about 1 metre above ground, plus several “catch” wires which are either 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 are 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.

Figure 3.4 Scott Henry System

Scott Henry Canopy

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. Thirty (30) cm separate 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 to 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.

Smart Dyson System

This system uses a single cordon with half the shoots allowed to be trained downward and half trained upward. Each shoot position is alternately train up and down. This had 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.

Horizontally Divided Canopy System

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). 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 are-as.

  • A divided canopy with shoot positioning:
  • reduces shading in the renewal zone;
  • doubles the canopy area;
  • provides good fruit and leaf exposure;
  • often increases yields;
  • improves wood and fruit quality;

may cause some sunburn on clusters near the top of the renewal zone.

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 4-week period after bloom; the second time in 2 to 3 weeks as the shoots again try to become horizontal.

Figure 3.5 Horizontally Divided Canopy System


Geneva Double Curtain

The Geneva Double Curtain (GDC for short) 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 metres apart and 1.8 metres above the ground. The system usually has two cordons of between 1.8 to 2.4 metres 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 pro-motes 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 sun-light, and maximum leaf and fruit exposure is maintained.

Wide T Trellis System

Similar in structure to the GDC it has two horizontal wires 0.9-1.2m 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 diffi-culty in working with the height of the canopy, and is not conducive to mechanical harvesting. Unless rows are very wide the growth causes problems with tractor movement.

Posts and Wire

The vine trellis is a structure that has to support large loads. The various load components include the vertical load which includes the weight of the fruit, vine and wire. The lateral load is com-posed 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 wooden posts 8-9 feet in length. They are long lived (20 years) and very strong and flexible. The use of 3-4inch posts for in row support and 4-5 inch or 5-6 inch for end posts is common practice. Metal posts may also be used and can be air vibrated into the soil but do not have the strength or flexibility of the wooden posts and are more expensive.

Anchor Systems

There are many systems in use to offer the strength for tensioning the trellis wire. A few examples include:

Angling the end posts 7-10° away from the planted side. This is then secured to a concrete block or some other ‘dead head’ buried in the soil. There are also anchors designed for rocky soil that can be driven into the earth and attached to the angled end post. The advantage of this type of anchor is the soil is not disturbed and offers immediate strength once attached. The end post should be driven into the soil one meter to ensure stability.

Braced assemblies – this is a brace between the end post (upright) and the ground. The lower the brace is on the end post the less likely the end post will be ‘jacked’ out of the ground. The brace should be at least 3 meters and have an angle to the ground of 25- 30°. It should also be set against a suitable base plate set in firm soil.

Horizontal box anchor – this consists of a pair of end posts 2-3 meters apart. A horizontal post or rail is fitted between the tops of the end posts. There is also a wire loop from the base of the end post to the top of the second post to stabilize the system.

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; they 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 anchor available, which works surprisingly 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!

Figure 3.6 Sample of a Braced Assembly without the Angled End Post