Canopy Management for Pacific Northwest Vineyards

Mercy Olmstead, Kathleen Willemsen, and Markus Keller

Growing grapes in the Pacific Northwest can be challenging and rewarding, and depending upon your location, vegetative growth and management will differ. Growers need to carefully assess their vineyard site including soil characteristics, annual precipitation, and precipitation timing in addition to researching potential grape varieties in order to assess potential vine vigor. 

Vineyard location can have a large effect on vine growth. Those located in maritime climates may be concerned with controlling vegetative growth and increasing fruit exposure; while those in inland Pacific Northwest vineyards may need to adjust their vegetative management to optimize their canopy and fruit exposure. However, proper canopy management can lead to good profits for the grower and high quality fruit for the winemaker.

Management of grapevine canopies has changed over the years, and throughout the world. Many European countries have adopted a tightly spaced, minimal height vineyard, with no trellis support, while some New World countries have moved to a wider spacing and trellis system. Benefits can be realized for both types of systems, and those in between, depending upon grape variety characteristics and climate. However it may behoove us to define some terms before talking specifically about canopy management for Pacific Northwest vineyards.

Definitions of Canopy Components 

Canopy, as defined in this publication, contains all vegetative and reproductive plant parts that are above-ground. This includes the trunk, cordons, canes, spurs (Fig. 4.1), shoots, fruit, and leaves. The management of this canopy involves the manipulation of these components in order to achieve a balance between vegetative and reproductive growth for optimum yield and fruit quality. 

Shoots are comprised of vegetative and reproductive growth containing the length from the basal end to the growing tip. The growing tip is where leaves are initiated during optimum growing conditions, and can be used as an indicator of vine stress. Shoots originate from buds, which occur on canes, spurs, cordons; trunk and even underground (emerge as suckers).

Canes are mature, lignified wood from the previous season’s growth. Canes and shoots are comprised of nodes (Figure 4.2), with spaces between nodes defined as internodes. At each node is a bud containing three sets of buds (primary, secondary, and tertiary). The primary bud is the most fruitful, while the tertiary bud is the least fruitful. Buds can be dissected before pruning to aid in determining the potential crop load and help with decisions about pruning severity. 

Pruning weight is determined by the amount of wood that is pruned off one vine in a single season. This can be used in formulas to determine how many buds should be removed and/or left on the vine as part of balanced pruning techniques (Reynolds, 1988). The amount of pruning wood is determined by how the canopy is managed throughout the previous season. Thus, if a vineyard is on a particularly vigorous site, then a large amount of pruning wood can be accumulated. However, on a low vigor site the canopy may be fairly small, leading to thinner canes and lower pruning weight.

Crop load is used to describe the ratio of yield to the pruning weight or leaf area. Potential crop yield before bloom can be determined by analyzing the primary, secondary, and tertiary buds (Morrison, 1991). This can then be used to adjust the pruning strategy to achieve optimum balance for fruit quality. 

The vigor of the vine describes the growth rate and depends on a combination of factors, including soil type, texture, depth, water availability, and variety choice. Inherently, some grape varieties are more vigorous (e.g., Syrah or Shiraz, Sangiovese) than others. Canopies of vigorous varieties can produce an excess amount of leaf area when compared to recommended levels and may require more intense management.

Most canopy management is directed at the manipulation of the canopy microclimate, which is the climate surrounding and within the canopy (Tarara, 2005). Microclimate includes a number of factors including solar radiation, temperature, wind speed, humidity, and evaporation rates. Because leaves tend to alter these factors, the canopy microclimate depends upon the number of leaves and their spatial arrangement within a defined area (Smart, 1985).

Figure 4.1 A typical cordon-trained grapevine and its associated sections before spur pruning

Figure 4.2 Shoot anatomy showing nodes, internodes, composite bud, and leaf scar.

Goals of Canopy Management

  • Establish and maintain vine shape into one which facilitates uniformity in growth and fruit production
  • Maintain vine shape to utilize mechanical means of vineyard tasks
  • Produce optimum quality fruit through manipulation of vegetative growth
  • Control crop load
  • Promote continuous production of fruitful buds where desired (depending upon trellising system)
  • Mitigate cold damage through the proper allocation of carbohydrate resources 

Light and Temperature Effects of Canopy Manipulation 

In order to understand how light and temperature affects vine growth, a brief review of some basic plant physiology is necessary. Plants fix carbon from the atmosphere through a process called photosynthesis. This process takes carbon dioxide from the atmosphere in addition to water and, using light energy, builds a carbohydrate molecule while giving off oxygen.

6CO2 + 6H2O Light Energy C6H12O6 + 6O2

Through photosynthesis, carbohydrate is fixed (sugars are produced), and energy is produced via respiration, which occurs continuously. During respiration, some of this carbon that has been fixed is used to make energy to drive other processes in the plant.

Plants need a certain quantity of light (measured in µmol photons/m2s) in order to achieve their maximum sugar production. In grapes, about 40% of full sunlight (800 µmol/m2s) satisfies the maximum photosynthesis requirement (Smart, 1988; Keller et al., 1998). For comparison, a bright sunny day in most of the Pacific Northwest will have about 2000 µmol/m2s, although this may vary according to your specific latitude and time of season. Light quality is also an important factor in plant growth, as leaves strongly absorb at peaks in the blue (430 nm) and red (660 nm) range . The range of the spectrum that plants use for photosynthesis is called photosynthetically active radiation (PAR), which is approximately the visible light range from 400-700 nm.

Grape leaves are very efficient at absorbing solar radiation, with over 85% of PAR absorbed by the outer layer of the canopy (Figure 4.3; (Smart et al., 1985). The remaining 15% is either transmitted through the leaf or reflected up to the atmosphere. Canopy structure determines the amount of light intercepted by exterior leaves. Beyond the first layer of leaves, only 10% of the PAR is reaching the interior, and further into the canopy, less than 1% of the sunlight reaches the interior of the vine (Smart, 1991). Sunlight interception by leaves can be via direct or diffuse radiation. Direct radiation interception by exterior leaves drives canopy photosynthesis more efficiently than interception of diffuse radiation (Smart, 1984; Smart et al., 1988). Leaf orientation within a canopy (i.e. perpendicular to angle of solar radiation) must be optimal to efficiently intercept solar radiation. 

Measurements of shade can be assessed by looking at the red:far red (R:FR) ratio. As mentioned above, leaves absorb red light (660 nm) and reflect light in the far red (730 nm) range (~41%) (Smart et al., 1988). As grapevine canopies become more shaded, a greater proportion of the light that reaches the interior leaves is far red light (Smart et al., 1982). Thus, the lower the R:FR ratio, the less efficient the leaves in the interior are at photosynthesis.

Effects on Low Light Quantity on Grapevines:

  • Decrease shoot growth, but increase lateral growth
  • Decrease fruit set
  • Delay in fruit maturity
  • Reduction in fruit color
  • Reduction in acid degradation 
  • Reduction in fruit cluster initiation for subsequent seasons
  • Increase in disease incidence
  • Increase in certain pest populations (e.g., leafhoppers)
  • Increase in internode length 

(Morgan et al., 1985; Keller et al., 1998; Keller and Hrazdina, 1998; Petrie et al., 2003) 

Temperature can also have a significant effect on shoot growth and fruit quality. Grape clusters and leaves in direct sunlight can experience temperatures 13-15°C higher than ambient temperatures (Spayd et al., 2002). This is why during a 40°C day summer day, fruit ripening slows down or can even stall. Typically, as temperatures increase, the rate of shoot growth increases. However, high temperatures (>35°C) can decrease shoot growth by shutting down photosynthesis (Ferrini et al., 1995).

Low temperature (<10°C) can also decrease grapevine growth by slowing photosynthesis. This can have a cascading effect on fruit set, fruit development and ripening, and storage of reserves in the grapevine for subsequent growing seasons.

Knowledge of the temperature differences between sites can be useful for matching site to variety and also determining ripening times. It is more important to grow appropriate varieties for specific sites than to grow mediocre quality grapes on inappropriate sites. Separate vineyards can be planted to stagger ripening times to ensure that deliveries to wineries will be handled in a timely fashion. This underlines the importance of site selection and communication between the grower and the winery.

Figure 4.3. Balance of solar radiation absorbed, transmitted, and reflected from a Gewürztraminer grape leaf.

Effects of Low and Very High Temperatures on Grapevine Canopies: 

  • Decrease photosynthesis, possibly leading to reduced sugar accumulation and reserves
  • Decrease shoot growth
  • Delayed ripening
  • Decrease fruit set

Canopy Assessment Methods 

Shading Indices

In upright canopy systems, the surface area of the vine is determined by the height and width of the full grown canopy. The greater the surface area, the more solar radiation is intercepted for growth processes. One thing to consider when assessing canopies is volume, which is determined by the height and width of the vines trained to a specific trellising system. The larger the volume, the greater the number of leaves, and shading may be a concern. One easy way to determine fruit exposure is to calculate the surface area to volume ratio. This can be easily done with a meter stick or measuring tape to derive the exterior canopy dimensions.

Point Quadrat

This method is another tool that can be used in conjunction with calculating shading indices and sunfleck analysis to assess canopy density. Point quadrat method requires a thin metal rod that is randomly inserted into the canopy. As with measuring leaf layer number (LLN), each leaf or other vine parts that touch the rod are recorded on a spreadsheet. Multiple areas within the canopy should be assessed, at least 50 to 100 times in order to get good, representative data (Smart, 1991). Be sure to avoid bias by choosing a uniform random method of inserting the rod throughout the vineyard row or block (e.g., every X number of steps). Record each leaf, cluster and canopy gap that the rod passes through from one side of the canopy to the other. 

Once you have recorded your information from the canopy assessment, you can calculate percent gaps (rod does not touch anything), leaf layer number, percent interior leaves, and percent interior clusters (Smart, 1991).

  • % gaps = total gap #/# of insertions x 100
  • LLN = total # of leaf contacts/# of insertions
  • % interior leaves = # interior leaves/total leaf # recorded x 100
  • % interior clusters = # interior clusters/total cluster # recorded x 100

Ideal numbers for this method should be 20-40% canopy gaps, LLN of 1.0-1.5, % interior leaves <10%, and % interior clusters <40%.

Sunfleck Analyses 

This method assesses the amount of canopy gaps, and can be done throughout the season. Estimate the proportion of gaps in the canopy, especially around the fruiting zone. There should be adequate light reaching the fruiting zone from the top or exterior portion of canopy to the cordon or cane. An easy way to measure this is to set a sheet or tarp underneath the canopy under the fruiting zone and assess canopy gaps within a defined area. This defined area can be drawn on the sheet (e.g., 1m2). When completed, the percentage of sun reaching the ground for vertical canopies should be between 2- 10% (Smart, 1973).

Techniques for Canopy Manipulations

Training System 

Training and trellis systems that allow for upright positioning of shoots (i.e., Vertical Shoot Positioning – VSP) generally allow adequate light penetration and air movement through the canopies of most grape varieties grown in the Pacific Northwest. However, these systems can allow too much fruit exposure in high-solar radiation inland areas, causing sunburn. In these areas, a system that allows for more shading (e.g., simple sprawl) can optimize fruit exposure. Divided canopy systems with hanging shoots, like Geneva Double Curtain or Scott-Henry are more apt to have more leaf area with a well-exposed fruit zone due to the positioning of shoots upwards and downwards, depending upon the specific system. Scott-Henry systems are especially good for those varieties and sites that can be particularly vigorous. However, when a divided canopy is used, yields increase due to the higher number of buds on the vine. In these cases, crop load must be carefully balanced with vegetative growth for optimum fruit quality. 

When laying out the vineyard, be sure to optimize light absorption by equalizing the height of the trellising system and the width between rows. This should result in a 1:1 ratio between rows and trellis height (Smart, 1982). This avoids the ‘bleeding’ through of light and inefficiencies in the vineyard regarding the capture of sunlight. However, if vineyard rows are too closely spaced, it is possible to get cross-row shading, which can lead to shaded leaves close to the fruiting zone.

Pruning 

Grapevines have a fixed capacity – that is one vine can ripen a certain amount of fruit and support a certain amount of shoots. One of the main goals of pruning is to ensure that there is enough potential vegetative growth to ripen the crop and enough fruitful buds to provide an adequate crop load. Large canopies can negatively affect fruit quality, with other negative effects on canopy quality (e.g., disease incidence and penetration of fungicides and pesticides). In addition, getting light into the canopy will help with forming fruitful buds for the following year, and help in hardening the canes off for the winter in the fall. 

Specific pruning recommendations will depend on your training system (i.e., spur or cane-pruned system), variety (e.g., some varieties do not produce fruitful basal buds and are cane-pruned), and vine vigor. In cordon-trained systems, 2-3 bud spurs should be evenly spaced along the cordon (Figure 4.4). In cane-pruned systems, be sure to choose canes that have adequate spacing between nodes for fruiting wood. Distinguish between count and non-count buds; only buds that are one finger width above the cordon should be counted in the final bud count for that spur (Figure 4.5). Buds close to the cordon are basal buds and usually remain dormant. Potential crop load can be determined by sectioning buds and is most often used before pruning to give an idea of buds that may be damaged by winter temperatures.

Balanced pruning may be used as a tool to adjust cropload in areas of variable vigor. This technique incorporates prunings from several representative vines and estimates the vines’ capacity based on the weight of these prunings. Thus, if a vine had weak growth the previous season, less buds would be left to encourage the vigor of the remaining shoots. A vigorous vine would benefit from a lighter pruning (more buds), thus balancing leaf area and crop load while decreasing the vigor of the remaining shoots.

The bud number to be retained is usually a minimum per vine plus a certain number for each pound. For winegrape varieties, numbers for balanced pruning will depend upon the variety (Smart, 1991). As a rule of thumb, leave about 30 buds per kg (15/lb) of pruning weight. 

One more thing to consider is the crop to pruning weight ratio. In much of the research literature, these ratios have been given for well-watered vines. It can be calculated from the kg/vine of fruit and dividing that by the kg/vine of pruned canes. This will give an idea of the balance of the vine. If this number is too low (<5), then the vine may be able to support more crop load than what was harvested from it last year, and bud numbers/vine can be increased per vine. If it is too high (>10), then perhaps the crop may need some thinning, or the bud number may need to be reduced per vine.

Figure 4.4 Evenly spaced spurs in a vertically-trained, cordon system.

Figure 4.5 Non-count buds are those less than one fingers width from the cordon as seen here in a spur-pruned, cordon-trained system.

Goals of Pruning 

  • Maintain a balance between vegetative growth and fruit growth (including regulation of bunch number and size)
  • Produce high quality fruit
  • Select nodes that produce fruitful shoots
  • Allow for easy access of farm equipment and vineyard traffic

Shoot Thinning

Often after bud break, a number of shoots will emerge from latent buds in the cordon in spur trained systems, or bud position may not be optimum in cane-pruned systems. Shoot thinning can be used to help improve the light penetration into the canopy later on in the season. This can also be used to adjust crop load by thinning fruitful shoots to reduce the crop, or thinning non-fruitful shoots to increase the leaf area to crop ratio.

Shoots can be removed once they have pushed out at least 10-15 cm in order to adjust the spacing between shoots. Spacing between shoots should be about 7 cm, with spurs remaining at 10-15 cm in order to get good light and air movement through the canopy. 

Shoot Positioning 

Although pruning is used to manipulate shoot position, shoot positioning can be used to direct shoot growth upwards or downwards. Shoots are usually tucked under a number of catch wires, depending upon your trellis design. The main goal of shoot positioning is to expose the fruit for color development (in red varieties) and increase air movement around the cluster to reduce disease incidence. The earlier berries and clusters are exposed, the less chance there is of inducing “sunburn”. Earlier exposure can induce the skins to develop secondary metabolites which are similar to melatonin production in human skin (a.k.a. your ‘suntan’), that protects the berry from harsh UV solar radiation. Be cautious of doing shoot positioning or leaf removal too late into the season, otherwise sunburn can be a problem, especially with white varieties.

Table 4.1 Influences of vineyard establishment and management on grapevine yield components 

Component

Determined During

Management Options

Vines / acre  Planting  Density / Trellis design 
Nodes / vine  Winter pruning Pruning level 
Shoots / node Budbreak -  Pruning level, short thinning, nutrition, canopy management
Clusters / shoot  Early previous season and current season   

Flowers / cluster

Berries / cluster 

Fruit set Nutrition, canopy management, irrigation, nutrition 
Berry weight All season 

Irrigation, nutrition, crop thinning

 

 

Methods to Improve Fruit Exposure 

Hedging

Canopies that are overly vegetative and large can reduce air flow and increase disease incidence, reduce light quantity, change light quality, and reduce fruit quality. Hedging can be used to remove the top portions of the canopy (10-20%) in order to reduce shoot growth and young leaves which can act as a strong sink for carbohydrates. However, timing is very important, as vines can compensate for the reduction in leaf area by compensating in growth elsewhere in the vine (i.e., lateral shoot growth) (Candolfi-Vasconcelos and Koblet, 1990; CandolfiVasconcelos et al., 1994). If hedging is done midway through fruit development (i.e., lag phase), then the vine has a better chance of developing those newly developed leaves to produce sugars, than later in the season (Cartechini et al., 2000). Late hedging will direct the vine’s energy to a new flush of lateral shoot growth, rather than to the developing fruit which can delay ripening. As with cluster thinning, if repeated hedging is necessary, it is time to revisit your pruning and crop load strategies. 

Leaf Removal

In vineyards where there is excess vigor or lateral growth, leaf removal can be practiced to increase fruit exposure to light and better balance vine and fruit growth. With this technique, leaves are removed in the bottom portion of the canopy (~30 cm), by either hand or mechanical means (Figure 4.7). 

Excess removal of leaves around the fruiting zone however, may delay ripening and reduce sugar accumulation. Leaves immediately around the cluster are important for sugar accumulation, and there is a period of adjustment in the vine to source sugars from other leaves further above on the shoot. Thus, timing of leaf removal is very important. Under warm conditions (e.g. interior PNW), timing of leaf removal has been shown to not affect yield components or fruit composition (Kliewer and Bledsoe, 1987).

Early leaf removal soon after fruit set seems to be the best time in order to get maximum benefit of increased exposure. Late leaf removal (i.e., around veraison) can increase the risk of sunburn in grape berries, because berries do not develop protective compounds to deflect harmful UV rays. Damage from UV rays can lead to reduced anthocyanin production and delayed ripening (Spayd et al., 2002). In addition, leaf removal should be concentrated on the east side of the vine in rows oriented north-south to avoid cluster overexposure on the west side of the vine.

Figure 4.6 Hedging

Figure 4.7 Leaf removal can be employed to get better light exposure and air movement into the fruit zone. Extreme leaf removal, if too late in the season as seen here, can leave clusters open to sunburn and may delay fruit ripening.

The Ideal Canopy

Based on a number of recommendations by Richard Smart (Smart, 1991), the ideal canopy can be defined by a number of characteristics. 

  • 1:1 canopy height to row width to avoid cross-row shading and optimize sunlight interception
  • North-south row orientation
  • Vertical training systems to maximize sunlight interception
  • 21,000 m2/ha of canopy surface area
  • Leaf area/surface area = < 1.5
  • Leaf layer number = 3.0
  • 7-14 cm2 leaf area per gram of fruit
  • 1.0-1.5 m shoot length
  • Internode length = 60-80 mm 
  • Yield : pruning weight = 5-10
  • 20-40% canopy gaps 

Although these recommendations are a good guide, be sure to take into consideration your vineyard site, grape variety, and vigor before comparing your canopy to the “ideal” canopy. Use your experience with particular varieties on particular sites to adjust or fine-tune these numbers as needed. The goal in any case should be to have the proper balance of vegetative and reproductive growth to optimize fruit quality and yield. 

Concluding Remarks 

Canopy management must start with proper site selection, soil evaluation, and variety choice. There are multiple points in the establishment of a vineyard to manipulate a number of factors that can enhance fruit quality.

References and Useful Literature 

Candolfi-Vasconcelos, M. C. and W. Koblet. 1990. Yield, Fruit Quality, Bud Fertility and Starch Reserves of the Wood as a Function of Leaf Removal in Vitis Vinifera - Evidence of Compensation and Stress Recovering. Vitis. 29: 199-221.

Candolfi-Vasconcelos, M. C., W. Koblet, G. S. Howell and W. Zweifel. 1994. Influence of Defoliation, Rootstock, Training System, and Leaf Position on Gas Exchange of Pinot Noir Grapevines. Am. J. Enol. Vitic. 45(2): 173-180.

Cartechini, A., A. Palliotti and C. Lungarotti. 2000. Influence of Timing of Summer Hedging on Yield and Grape Quality in Some Red and White Grapevine Cultivars. Acta Horticulturae. 512: 101-110. 

Ferrini, F., G. B. Mattii and F. P. Nicese. 1995. Effect of Temperature on Key Physiological Responses of Grapevine Leaf. American Journal of Enology and Viticulture. 46(3): 375-379. 

Keller, M. 2001. Principles to Have in Mind When Deciding on a Thinning Strategy. Australian Viticulture. 5: 27-29. 

Keller, M., K. J. Arnink and G. Hrazdina. 1998. Interaction of Nitrogen Availability During Bloom and Light Intensity During Veraison. I. Effects on Grapevine Growth, Fruit Development, and Ripening. American Journal of Enology and Viticulture. 49(3): 333-340. 

Keller, M. and G. Hrazdina. 1998. Interaction of Nitrogen Availability During Bloom and Light Intensity During Veraison. Ii. Effects on Anthocyanin and Phenolic Development During Grape Ripening. American Journal of Enology and Viticulture. 49(3): 341-349.

Kliewer, W. M. and A. M. Bledsoe. 1987. Influence of Hedging and Leaf Removal on Canopy Microclimate, Grape Composition, and Wine Quality under California Conditions. Acta Horticulturae. 206: 157-168. 

Morgan, D. C., C. J. Stanley and I. J. Warrington. 1985. The Effects of Simulated Daylight and Shade-Light on Vegetative and Reproductive Growth in Kiwifruit and Grapevine. Journal of Horticultural Science and Biotechnology. 60(4): 473-484.

Morrison, J. C. 1991. Bud Development in Vitis Vinifera L. Botanical Gazette. 152(3): 304-315. 

Petrie, P. R., M. C. T. Trought, G. S. Howell and G. D. Buchan. 2003. The Effect of Leaf Removal and Canopy Height on Whole-Vine Gas Exchange and Fruit Development of Vitis Vinifera L. Sauvignon Blanc. Functional Plant Biology. 30: 711- 717.

Reynolds, A. G. 1988. Response of Riesling Vines to Training System and Pruning Strategy. Vitis. 27: 229-242. 

Smart, R. E. 1973. Sunlight Interception by Vineyards. American Journal of Enology and Viticulture. 24(4): 141-147. 

Smart, R. E. 1984. Some Aspects of Climate, Canopy Microclimate, Vine Physiology, and Wine Quality. Proceedings of the First International Cool Climate Viticulture and Enology Symposium., Oregon State University, Corvallis.

Smart, R. E. 1985. Principles of Grapevine Canopy Microclimate Manipulation with Implications for Yield and Quality. A Review. American Journal of Enology and Viticulture. 36(3): 230-239.

Smart, R. E. 1988. Shoot Spacing and Canopy Light Microclimate. Am. J. Enol. Vitic. 39(4): 325-333. 

Smart, R. E. 1991. Sunlight into Wine: A Handbook for Winegrape Canopy Management. Adelaide, AU, Winetitles.

Smart, R. E., J. B. Robinson, G. R. Due and C. J. Brian. 1985. Canopy Microclimate for the Cultivar Shiraz. I. Definition of Canopy Microclimate. Vitis. 24: 17-31.

Smart, R. E., N. J. Shaulis and E. R. Lemon. 1982. The Effect of Concord Vineyard Microclimate on Yield. I. The Effects of Pruning, Training, and Shoot Positioning on Radiation Microclimate. Am. J. Enol. Vitic. 33(2): 99-108. 

Smart, R. E., S. M. Smith and R. V. Winchester. 1988. Light Quality and Quantity Effects on Fruit Ripening for Cabernet Sauvignon. Am. J. Enol. Vitic. 39(3): 250-258. 

Spayd, S. E., J. M. Tarara, D. L. Mee and J. C. Ferguson. 2002. Separation of Sunlight and Temperature Effects on the Composition of Vitis Vinifera Cv. Merlot Berries. Am. J. Enol. Vitic. 53(3): 171-182. 

Tarara, J. M. 2005. A Climatology Refresher for Vineyard Managers and Winemakers. WSU Wine and Grape Research and Extension Newsletter. Prosser, WA. 15: 2-5.

Pruning

Pruning is the single most influential activity affecting vine growth, fruit quality and winter survival. The objective of pruning is to balance the development above ground to the vigor and development of the root system, maintain the vine shape while replacing injured or warn out areas.

Each vine has a fixed capacity potential to ripen a given quantity of fruit and wood depending on the vine’s root system, vine size, leaf area, number of fruitful shoots, variety, climate, soil, trellis system and vineyard management. Overpruned vines produce less fruit, excessive vigor causing shading and are prone to injury from cold temperatures. Light pruned vines produce large numbers of shoots, large numbers of bunches and poor quality of fruit.

There are various types of trellis systems as shown in Section 3.5 but only two methods of pruning. These differ in the length of one year old wood retained after pruning. Cane pruning retains long fruiting canes filling the space between plants. Spur pruning utilizes short canes (1-2 buds) originating from a cordon system that fills the space between plants. 

The decision of which system of pruning to employ will be dependent, in part, on the fruitfulness of the basal buds vs. the fruitfulness of the buds occurring in mid-cane.

Prior to the beginning of pruning it is useful to check for primary bud damage. This is accomplished by using a thin blade and cutting through the bud parallel to the cane. A live bud is green while a dead bud is brown dark in color. Care should be taken not to cut too deep or the green tissue underneath the bud will be exposed. This can be green even if the bud is dead. Buds should be checked on a number of long canes to get an understanding of any winter damage. 

When pruning, select canes of pencil thickness, uniform diameter, and uniform color and free of disease. Canes must also be well hardened and have grown with good sun exposure. It has been shown that late pruning delays bud break. This is useful if any areas are prone to late season frosts.

A guide to bud numbers is to use the fruit weight to pruning weight ratio. (This concept is explained in Vine Physiology Section 2 and Canopy Management Section 4.2) A low ratio of 4-5 suggests more buds should be left and a high ratio suggests fewer buds should be left. 

Cane Pruning 

The canes should originate close to the main trunk and 10-20 cm below the fruiting wire. Canes growing directly from old wood should be avoided if possible as they are not as fruitful. A single short spur in good position near the main trunk can also be left to grow the fruiting canes for next year.

The number of buds left depends on vine spacing, the number of buds producing in the previous year and the growth attained. If the growth is weak, leave fewer buds and if strong, leave a few more buds. 

Canes are cut through the last node when pruning to facilitate typing. Some individuals prefer to wrap the cane around the wire to reduce the amount of tying required. Cane pruned vines must be tied each year. 

Spur Pruning 

Spur pruning is restricted to vines which are cordon trained. Spurs consist of 1-2 buds not including the very basal bud. Two to 3 spurs can be left if increased crop is desired. These nodes produce the shoots and fruit for the current season’s growth. Basal buds may often be unfruitful if they are shaded or if shoots are over vigorous. Spur pruned vines require good leaf and shoot management to expose basal buds to sunlight during the period of fruit bud initiation (around bloom and a few weeks after bloom). Good light conditions are required for these buds to develop the flower clusters and flower parts for the next year’s crop. Spur pruning can be used for any variety with fruitful basal buds.

Spur pruning is quicker and more economical. However it is easy to over crop vines and to create shading and crowding of fruit clusters when too many nodes are left. Summer shoot thinning may be required to correct ‘mistakes’.

Spurs are usually left in a vertical position, except for vines trained to the Geneva Double Curtain or spur pruned Scott Henry system. Tying of spur pruned vines is required only when new cordons are established or when an arm breaks free of the original tie. 

Cordon trained vines use the same trellis system as cane pruned vines.