A common problem with grape vines is how to train vines to prevent overlapping foliage in order to allow sufficient sun exposure. It is well known that shading has adverse effects on fruit quality. When their leaves are shaded, grape vines suffer from higher acidity, impaired color, and lower soluble solids and phenolic content.
To illustrate the limitations of current growing methods, a conventional grape vineyard training system known as the Vertical Shoot Positioning (VSP) system will be described in this section.
In order to increase exposure to the sun's rays, vines are commonly attached to a framework called a trellis. A new growth is called a shoot and collectively, all the shoots comprise the canopy. The canopy is held in position using high tensile wire attached to posts.
FIG. 1A shows a typical Vertical Shoot Positioned canopy attached to trellis 10. Of all the variations of trellis systems the “Vertical Shoot Positioned ” system is one of the most common for high quality wine grapes. The leaves of the shoots have been omitted for clarity. The vine trunks 50 are trained to terminate at the lowest wire called the fruiting wire 40. From that point, extensions of the trunk called either cordons or canes 60 are tied to the fruiting wire. New seasonal growth emerges from these cordons or canes. This growth is called a shoot 70. As these new shoots grow they follow random paths searching and competing for sunlight. In an attempt to keep the shoots from shading each other and from shading the emerging grape clusters the grower positions each shoot within catch wires 30 and enables it to grow vertically upwards. Keeping the shoots separated from each other and within their own space within the catch wires is the goal.
In FIG. 1A the vine shoots 70 have been positioned inside the catch wires 30 but can still lean along the axial direction of the fruiting wire resulting in leaf on leaf shading and crowding. The figure illustrates shoots bunching together along the catch wires and near the posts. This causes a shading problem.
There are a limited number of ways that the shoots are initially positioned within the catch wires. Positioning each shoot by hand, one at a time, is common practice. With tens of thousands of shoots per acre this is very slow and time consuming.
Another way to position the shoots is by using movable catch wires. This method is faster than hand positioning but still allows the shoots to move along the fruiting wire axial direction within the confines of the catch wires after positioning takes place. Catch wires 30 can be removed and replaced on the posts 20 through the use of post clips 80.
Although the current systems have many advantages over non-positioned vines they also have several inherent disadvantages. First, existing shoot-positioning methods are very labor intensive. After the initial positioning of the shoots one or two additional passes are usually required to keep the shoots separated and reinserted between the catch wires.
Furthermore, environmental conditions such as wind move the shoots in the fruiting wire axial direction within the catch wires resulting in a non-uniform distribution of shoots along the trellis. This results in congested areas of foliage that shade each other and lower the overall quality of the canopy. Remedial measures to correct this problem are commonly made by using trellis clips that pinch the catch wires together at one or more locations between posts. This prevents the shoots from moving sideways but contribute to additional bunching and shading of the shoots.
Another problem with conventional systems is that some shoots move within the catch wires 30 enough to escape the confines of the catch wires resulting in additional labor to reposition the foliage by hand.
On a smaller scale, there are commercial grid products designed for supporting flowers or small plants, and cannabis. The flower and small plant products are round or have length to width ratios limited to about three to one, whereas grapevine trellises are highly linear and can extend hundreds of lineal feet or as required to form an extended grapevine canopy. Garden grow thru grids are made with fixed legs or fixed height restrictions and so cannot be adjusted to the dynamic growth habits of grape vines. The plant height and growth they are designed for are an order of magnitude smaller than that required for vineyards. They are limited to collecting plant shoots in the upward vertical direction only whereas grape shoots start budding several feet off the ground on a fruiting wire, and can be trained in any direction, including upward, downward and diagonally. Further, they cannot be used on a trellis system such as a grape trellis or be used in a mobile fashion to spread and hold foliage apart in order to achieve more plant sunlight exposure.
The other kind of available grid-based system is used for cannabis training. A system of strings or wires are used to form a grid configuration that is randomly configured in size and is used to hold down foliage branches so as to force the plants to grow sideways. Such configuration is not mobile throughout the range of shoot growth but is made to bear downward on foliage and suppress upward growth. This system has eventual growth of buds upward through the grid openings but this is an inconvenience of the system as the buds are then necessarily cut away and separated from the grid at harvest. The grid is discarded.
These limitations demonstrate that flower and cannabis support systems are inappropriate for training grape vines, and, as shown above, conventional grape vine training systems are not effective in preventing foliage shading. These problems are overcome by a new proposed training system described in the following sections. When the new method is applied to trellised grape vines, it is preferably referred to as the Vertical and Lateral Shoot Positioning (or VLSP) system.