Mark Chien, Pennsylvania State University
The two management areas that can most affect the outcome of grape quality in a growing season are proper canopy and fruit zone management. This article focuses on canopy management: what it is, how it’s done, and when it makes economic sense.
Canopy and yield management begin before vineyard establishment. The concept of vine size and balance are important to achieving a manageable canopy and fruit zone. The grower is trying to balance the vegetative and reproductive processes of the vine, and the first steps are choosing the correct site, correct cultivar/rootstock, and the correct vine spacing.
On a site with deep, fertile soils with high water holding capacity, it is likely a large vine will emerge with lots of foliage and fruit, which meets the needs of larger production vineyards. In winegrape production, a small- to moderate-sized vine is preferred, where energy is used less on producing leaves and more on ripening fruit. In any production scenario, a balanced vine is required to produce optimum fruit quality that a given site will support, and will define the wine style and price point objectives.
Vines have to be managed according to the targeted style and price point of the wine being produced. In the best of all worlds, the resulting vines are in perfect balance and very little intervention or manipulation must be done, but this is the rarely the case. Canopy management is necessary in inverse proportion to the qualities of the vineyard site - poorer sites usually require more intervention. In the absence of natural canopy and crop balance, the grower must apply viticultural practices to guide the vine and fruit into balance, with the result being perfectly mature fruit for wine making. Winegrape growers have two key objectives:
In practice, canopy management involves:
Good canopy management begins with careful and proper vine training with special considerations given to canopy architecture, such as overall canopy height and fruit wire height. These dimensions will have great implications for the performance of canopy and fruit. The choice of training and trellis system, e.g. cane or cordon, VSP or high wire, single or divided systems, will impact canopy design, performance and management.
Pruning sets the tone for canopy and crop levels. Pruning severity will affect just about every parameter of the canopy during the growing season from shoot number and length, to distribution of shoots and clusters within the canopy. Pruning is the first attempt in the season to balance the vine’s foliage with the crop size. See these articles on pruning and vine balance for more information.
As shoots begin to grow, suckering and shoot thinning allow the grower to adjust shoot numbers to achieve optimal distribution, density and leaf area to ripen the expected crop. It improves canopy configuration by limiting shoot density and is the first effort after bud break to regulate crop size. See more on shoot thinning.
Shoot positioning will improve the canopy performance of almost any training system, whether single or divided, vertical or horizontal. As with shoot thinning, shoot positioning seeks to improve canopy configuration and reduce the amount of shading created by overlapping shoots.
Wire moving is also a key part of shoot positioning. If it is done properly and in a timely manner, it can greatly enhance canopy architecture and reduce the amount of hand positioning needed. Timing is probably more critical for wire moving than any other canopy management practice. Wires are moved when shoots are rapidly growing. If done too early, the shoots will not stay in place. If too late, it becomes necessary to bend and tuck shoots, which often leads to breakage. Movable catch wires are preferred over fixed wires so they can be pulled away from the canopy and used to sweep shoots inside the wire and into an upward position. In most cases, two to three pairs of movable catch wires are adequate for this task. Shoots can be held in place with wire, plastic clips, or branch locks.
The purpose of leaf removal is to open up the interior of the canopy to light and air to help promote fruit ripening, reduce disease pressure and increase spray coverage. If conducted correctly, the benefits to grape quality can be dramatic as exposure can enhance fruit and wine flavor, color and wine texture.
Cooler regions tend to pay much closer attention to leaf removal, early in the season for disease control and later for fruit ripening benefits. In some cool areas such as Long Island of New York or the Willamette Valley of Oregon, as the ripening period stretches into mid- to late October and the sun lowers on the horizon and days are cool, the fruit zone will be completely stripped of leaves to increase the temperature of the berries. The additional heat helps to drive temperature-dependent metabolic processes responsible for the maturation of flavor, color, and phenolic compounds, as well as continue to dissipate methoxypyrazines.
In hot areas, leaves are retained to provide shade and a cooler environment for fruit and may be removed later in the season, even after veraison as the temperatures become cooler, but always with the threat of sunburn if there is an unexpected heat spike.
Leaf removal can also take the form of lateral removal, which is sometimes preferred to retain basal leaves that protect fruit from sunburn while opening the interior of the canopy. Tunneling is a practice where lower, interior leaves are removed. This must be done by hand and is time consuming and expensive. It may be required where vines have high vigor and bigger canopies.
There are a variety of mechanical leaf removers with different removal mechanisms: pulsed air bursts to shred leaves, fans and blades that cult leaves, and rollers that pull leaves into cutting knives. The trick is to remove the correct amount of leaves in the proper location and avoid damaging fruit in the process. It is easy to bruise berries if they are brushed by a hand or machine, depending on the stage of application.
On a vertical shoot position system, other late-season canopy management practices include hedging, often on the sides and top of the canopy. The application of bird nets will also have an effect on canopy configuration and needs to be taken into consideration.
It may be necessary to repeat these canopy management practices later in the season to achieve the desired effect. For example, leaf removal may require an early, mid- and late-season pass. Crop thinning may also require multiple passes to get the crop size just right.
Insect, disease, and other abiotic causes such as frost, hail, lightning, and wind damage will also impact the vine canopy during the growing season and must be accounted for when considering the amount of leaf area necessary to ripen the grapes. If excessive damage occurs, the crop must be adjusted to reflect the remaining foliage’s ability to fully ripen that fruit.
Canopy and fruit zone management are two distinct concepts and practices that are intertwined and anything done to one will affect the other. Crop size can affect vigor of a vine and is sometimes used to slow down vegetative growth. The canopy represents the solar panels that catch sunlight to convert to sugars and enhance ripening. The sugars also are used for energy to drive plant metabolic processes, including those that synthesize flavor, color, and phenolic compounds that characterize each variety. Manipulation of the canopy has a direct effect on fruit chemistry, composition, and quality.
Smart, Richard and Mike Robinson. 1991. Sunlight into Wine: A Handbook for Wine Grape Canopy Management. Winetitles.
Wolf, Tony. Wine Grape Production Guide for Eastern North America. 2008. Natural Resource, Agriculture, and Engineering Service.
Hellman, Edward W. Oregon Viticulture. 2003. Oregon State University Press.
Dr. Mark Greenspan, a viticulture consultant in California, has written numerous fine articles on the topic.
Dr. Richard Smart is an innovator in canopy management techniques.
Pruning, Training, and Canopy Management, Iowa State University
Sustainable Grape Productivity and the Growth-Yield Relationship: A Review - American Journal of Enology and Viticulture, 2001
Canopy Management, Texas A&M University
Canopy Management Can Alleviate Green Flavors in Wine, Cornell University
Reviewed by Patty Skinkis, Oregon State University
and Eric Stafne, Mississippi State University