Skye Earley (OMAFRA Summer Student) and Kathryn Carter (Fruit Specialist, OMAFRA)
Growing high quality grapes involves balancing fruit production with vegetative growth. Early season canopy management involves a variety of techniques that alter the number or position of shoots or leaves to make vines more manageable and improve quality and productivity (Smart, 1992).
Benefits of Canopy Management
Last year’s harvest was a reminder of just how challenging mother nature can be for grape growers. Frequent rainfall, and high humidity created intense disease pressure from late season fruit rots. While there is little that growers can do about the weather, practices such as early season canopy management can help mitigate the negative impacts of weather on the crop. Canopy management can reduce canopy congestion allowing for better air circulation and spray coverage resulting in reduced disease pressure (Vance et al.,2013). A more open canopy also allows for better light penetration which is critical for fruit quality this year and fruit set for next years’ crop. There are a variety of canopy management methods including shoot thinning, shoot positioning, early leaf removal and hedging.
Shoot thinning (Figure 1) involves removing/thinning selected shoots to create a well-balanced, open canopy. Shoot thinning reduces the canopy density resulting in increased air flow and reduced disease pressure. Opening the canopy also results in an increase in light penetration resulting in better sunlight exposure to fruit.
Shoot thinning should be done when shoots are 12 to 30 cm (5-12 inches) in length (Smith & Centiari,2017). If performed too late, the shoots can become lignified at the base and are difficult to remove, resulting in increased risk of vine damage and higher labour costs. 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). Shoots that are weak, secondary, tertiary, non-fruitful or arising from the trunk (that are not being used for trunk renewal) should be the first to be removed. Optimally equal spacing along the cordon between shoots should be retained to promote a well-balanced canopy. Shoot thinning can be more challenging in years with winter injury, due to lack of uniformity of bud development.
Fig.1 Shoot thinning a grape vine.
Shoot positioning involves changing the orientation of the shoots so they grow vertically up or down creating an open and uniform canopy. Opening the canopy helps to improve air circulation, resulting in a decrease in disease pressure. Proper shoot positioning also helps to increase sunlight penetration into the canopy, minimizing shading of the fruit and optimizing productivity the following year. Uniform canopies also make it easier to for mechanical hedging and leaf removal.
Shoot positioning is usually conducted one to two weeks after bloom, before the tendrils become firmly attached to avoid breakage and optimize labour efficiency (Striegler & Jones, 2019). Positioning is usually completed by hand, however there is specialized equipment available that can space out the shoots. Generally, two or three shoot positioning passes are required to provide optimal canopy management.
While shoot positioning is important in all training systems, proper positioning is critical in low cordon systems (Vertical Shoot Positioning or VSP) where canes are pushed upward and “tucked” between a set of catch wires. (Paolo, 2020). This process is completed several times during the growing season as shoots develop. In high cordon trellis systems such as Geneva Double Curtain (GDC), the shoots need to be positioned in such a way that they grow down and away from the cordon. This process, known as “combing”, reduces the vigour of shoots to assist in obtaining the preferred canopy density (Paolo, 2020).
Early Leaf Removal
Early leaf removal involves removing leaves from the area around the grape clusters from the pre-bloom to pea sized berry stage of development. Research suggests that leaf removal at bloom limits the carbohydrate food source for inflorescence, resulting in reduced berry size and limiting the number of berries per cluster resulting in a decrease in cluster compactness.
Decreased cluster compactness results in improved air ventilation within the cluster, helping to reduce disease pressure (Botrytis rot infections) in tight cluster varieties such as Pinot noir, Riesling, Chardonnay and Vignoles (Centinari, 2021). Early leaf removal also helps to improve light penetration to fruit increasing total soluble solids (TSS and Brix) and anthocyanins (impacting colour intensity) while lowering methoxypyrazines which cause herbaceous aromas.
When considering using early leaf removal, remember that there are no set recommendations for how many leaves need to be removed in order to impact fruit set. The impact of early leaf removal on fruit set is affected by shoot length and the shoot leaf area at the time of removal.
Weather conditions can also impact the effects of leaf removal, with extended periods of hot (>32oC) or wet, cool (<15oC) weather following leaf removal resulting in poor fruit set. Removing too many leaves during early leaf removal can also impact carbohydrate production in the leaves, potentially having a negative impact on cold hardiness.
Early season canopy management plays an important role in reducing canopy congestion, improving air circulation and increasing light penetration. Shoot thinning, shoot positioning and early leaf removal are early season canopy management techniques that can help improve spray coverage, reduce disease pressure and improve fruit quality. Canopy management required will vary between sites depending on cultivar, soil composition and training systems.
References and Resources
Hickey, C. (2019, April). Vineyard canopy management: Shoot thinning. University of Georgia extension (Publication 1152). Vineyard Canopy Management: Shoot Thinning | UGA Cooperative Extension
Paolo, S. (2020, June 4). Canopy management approaches between bloom and fruit set. Presentation for Michigan State University Grape Meeting.
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/
Striegler, K. & Jones, T. (2019, June 20). Canopy management: Shoot positioning. National cooperative extension. Canopy Management: Shoot Positioning – Grapes (extension.org) Vance, A.J., Reeve, A.L, & Skinkis, P.A. (2013, June). The role of canopy management in vine balance. Oregon State University. The Role of Canopy Management in Vine Balance | OSU Extension Catalog | Oregon State University