Early Season Canopy Management for Grapes: Shoot Thinning

By Spencer Leidl (summer student) and Kathryn Carter (OMAFRA)

As a new growing season begins, it is important to ensure the best possible growing conditions for grapes. There are many different steps needed to prepare the vines to bear fruit, one of which is early canopy management. Over the next two articles, we will touch on early season canopy management for grapes, its purpose, and some common techniques used in the industry.

What is Early Season Canopy Management?

Canopy management is one of the most important factors in determining grape quality in a vineyard. Canopy management can be defined as the range of techniques used by a grower on their vineyard which results in an altered amount of leaves, shoots, or fruits in a space to make a vine easier to manage and more productive (Smart,1992). In a commercial vineyard, the goal of production is to have an adequate canopy size with as little need for maintenance as possible, while also producing high quality fruit. Early season canopy management uses shoot thinning, shoot repositioning, and leaf removal to manage the canopy and ensure adequate sunlight.

Benefits of Early Season Canopy Management

Canopy management helps to open the canopy, resulting in improved airflow to the vines and reduced disease pressure. Increased airflow also makes it easier for pesticides to penetrate the canopy providing better control of pests (Vance et al.,2013). Canopy management also increases sunlight penetration to the basal leaves. In a very dense canopy, sunlight cannot reach the basal leaves effectively, causing the plant to expend energy on leaves which are not producing energy in return. When the canopy is thinned, more leaves and the fruit itself will be able to receive adequate sunlight (Vance et al.,2013) resulting in improved fruit composition and varietal character, increased bud fruitfulness and improved winter hardiness.

There are many different techniques that can be used in vineyards for early canopy management. This article will focus on shoot thinning and suckering trunks, and a subsequent article will focus on shoot positioning and early leaf removal.

Shoot Thinning/Suckering trunks

Shoot thinning involves decreasing shoot density to create a well-balanced canopy. Thinning is one of the first canopy management practices of the season and should be completed when the shoots are 5-18 inches long (Smith & Centiari,2017) before the tendrils grab neighbouring shoots, but after the threat of frost. The timing of shoot thinning is important, as the longer shoots become, the more difficult they are to remove, potentially resulting in damage to the vine. If shoot thinning is performed before inflorescences (clusters) are visible, increased growth of shoots and lateral growth may result in increased shading. The presence of inflorescences are needed to determine fruitful and unfruitful shoots while thinning. It may be of benefit to shoot thin early bud-breaking cultivars (e.g., ‘Chardonnay’, ‘Merlot’) earlier than late-breaking cultivars (e.g., ‘Cabernet Sauvignon’) due to differences in shoot growth.

When shoot thinning vinifera cultivars it is recommended to leave 3 to 5 shoots per linear foot of canopy (retain more shoots in white varieties than in red), and many hybrid cultivars require 4-6 shoots per foot (Smith & Centiari,2017) or 24 to 36 shoots per vine in vineyards with between-vine spacing of 6 feet (Hickey, 2019). Shoots that are weak, secondary, tertiary, non-fruitful or arising from the trunk that are not renewal should be the first to be removed. The position of the shoots along the cordon is important and retained shoots should be equally spaced to promote a uniform, balanced canopy.

Literature suggests that shoot thinning regardless of timing (pre or post bloom) can reduce leaf layer numbers and improve sunlight penetration (Reynolds et al. 1994). Research has shown that thinning after bloom appears to be superior to early season thinning in terms of leaf layer number, leaf exposure, cluster exposure, and reduction of lateral shoot growth. Delaying shoot thinning has been shown to have positive impacts on canopy microclimate, but these effects are not of a great enough magnitude to influence wine quality (Reynolds et al., 2005).

Benefits of Shoot Thinning

Shoot thinning reduces the canopy density resulting in:

• better air movement resulting in reduced disease pressure and improved drying and fungicide penetration.
• reduction in fruit shading, resulting in improved sunlight exposure to fruit and improved bud fruitfulness.
• improved balance of vegetative growth and fruit production (ie. Increased leaf area to crop ratio by removing non-fruitful shoots)
• reduction in shoot density and number of clusters per vine, which helps to moderate the crop yield and bring the vine closer to “balance”

 

Shoot thinning in a vineyard (K. Carter, OMAFRA).

 

Conclusion

Shoot thinning is a valuable tool in managing the orchard canopy to improve air circulation, minimize disease pressure, improve fungicide penetration, reduce shading, manage crop yields and balance vegetative growth and fruit production. Shoot thinning and canopy management techniques will vary between sites depending on cultivar, soil types and training systems. Grower experience is the best tool to determine what is best for their own individual crop.

 

Reference

Chien, M. (2019, June 20). Fundamentals of canopy management. National cooperative extension. https://grapes.extension.org/fundamentals-of-canopy-management/.

Hickey, C. (2019, April). Vineyard canopy management: Shoot thinning. University of Georgia extension (Publication 1152). https://secure.caes.uga.edu/extension/publications/files/pdf/C%201152_1.PDF.

Reynolds, A. (1989). Riesling vines respond to cluster thinning and shoot density manipulation. Journal of the American Society for Horticultural Science, 114, pp.364-368.

Reynolds, A. (1994). Shoot density affects Riesling grapevines: I. Vine performance. J. Am. Soc. Hortic. Sci, 119 pp.874-880.

Reynolds, A., Molek, T. and De Savigny, C. (2005). Timing of Shoot Thinning in Vitis vinifera: Impacts on Yield and Fruit Composition Variables. American Journal of Enology and Viticulture, 56, pp.343-356.

Smart, R.E. (1992). Canopy management. Viticulture volume 2, practices. Winetitles.

Smith, M. & Centinari, M. (2017, May 19). Early season grapevine canopy management, part I: Shoot thinning. Penn State extension wine & grapes U. https://psuwineandgrapes.wordpress.com/2017/05/19/early-season-grapevine-canopy-management-part-i-shoot-thinning/.

Vance, A.J., Reeve, A.L, & Skinkis, P.A. (2013, June). The role of canopy management in vine balance. Oregon State University. https://catalog.extension.oregonstate.edu/em9071.

Vanden Heuvel, J. [Cornell SIPS]. (2014, May 26). Vineyard management: Shoot thinning [Video]. Youtube. https://www.youtube.com/watch?v=5wyFolawc-s\.