Different Grape Types
Two types of grapes are grown commercially in Washington state:
- American grapes, Vitis labrusca and
- European grapes Vitis American grapes represented by the cultivar Concord are used primarily for juice making.
A small acreage supports the variety Niagara, a white labrusca type. Eleven cultivars of vinifera grapes are used exclusively for making wine. Another small acreage grows European type table grapes, which are harvested by hand. Almost all labrusca grapes are mechanically harvested. Many vinifera types also are harvested mechanically. Take mechanical harvesting into consideration when designing trellising and training systems for grapes.
The grapevine does not have a rigid trunk; there- fore, some support structure, usually a trellis, must be provided. The trellis design should provide maximum light penetration for the buds and clusters, especially in the later part of the growing season, while exposing a large percentage of the leaves to sunlight. The grape trellis is a major long-term investment. Before designing a trellis, growers must consider all those factors that may affect vine growth and management, e.g., irrigation systems, variety, vine vigor, mechanical pruning, and mechanical harvesting.
A good trellis should have some or most of the fol- lowing characteristics:
- strong and long-lived;
- supports the trunk, cordons, arms, spur, canes, and foliage;
- provides the maximum exposure of leaves and buds to sunlight;
- economical to construct;
- easy to repair and maintain;
- permanent with little need for annual maintenance; and
- adaptable to modern mechanical pruning and harvesting
Several kinds of trellises and training systems are in use in Washington. Growers are trying new ones. Primary differences among these are in height, number and location of wires, use of horizontal wire spreaders, posts for support of wires, end posts, and anchorage for end posts.
Single wire system
Seven-foot posts having a minimum top diameter of 3 to 4 inches are spaced about 18 to 21 feet apart (every three plants). Line posts must be buried at least 2 feet in the ground for adequate support. A single #9 wire is then placed across the top of the post, 5 feet above the ground (Figure 1). Grapes are cordon trained along this wire in both directions. They also can be cane pruned but this is not common in Washington.
This system is least expensive of all trellising systems. It is adapted to mechanical harvesting, and is used for Concord grapes. It does not offer full exposure of foliage to sunlight for vigorous varieties.