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 vigour.
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.
Canopy — all vegetative and reproductive plant parts that are above ground. This includes the trunk, cordons, canes, spurs, 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 — 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 — mature, lignified wood from the previous season’s growth. Canes and shoots are comprised of nodes, 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 making decisions about pruning severity.
Pruning weight — 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. 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 vigour site, the canopy may be fairly small, leading to thinner canes and lower pruning weight.
Crop load — 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. This can then be used to adjust the pruning strategy to achieve optimum balance for fruit quality.
Vigour — the vine growth rate, which 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. Microclimates include 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.
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. For comparison, a bright sunny day in most of the Pacific Northwest will have about 2000 µmol/m2s, although this may vary according to the 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. 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 reaches the interior and, further into the canopy, less than 1% of the sunlight reaches the interior of the vine.
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. 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 to 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%). As grapevine canopies become more shaded, a greater proportion of the light that reaches the interior leaves is far red light. 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 include:
Sunscald causes grape berry surfaces to become brown and possibly shriveled. These symptoms appear on the portions of the cluster exposed to direct sunlight.
This injury often occurs when fruit that has developed in shade is exposed to direct sunlight, such as when leaf removal, summer pruning, shoot positioning or other canopy management practices occur in mid- to late-season. Fruit exposed to sunlight for the entire growing season may also develop sunscald when drought conditions develop.
Fruit damaged by sunscald may develop various fruit rots and deteriorate further.
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. 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 can decrease shoot growth by shutting down photosynthesis: photosynthesis declines rapidly above 30°C and falls to nearly zero at 45°C.
Low temperatures (< 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.
Effects of low and very high temperatures on grapevine canopies include:
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 metre stick or measuring tape to derive the exterior canopy dimensions.
This method is another tool that can be used in conjunction with calculating shading indices and sunfleck analyses 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 part that touches 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.
Be sure to avoid bias by choosing a uniform random method of inserting the rod throughout the vineyard row or block, such as 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.
Ideal numbers for this method should be:
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, for example, 1 sq m. When completed, the percentage of sun reaching the ground for vertical canopies should be between 2-10%.
Training and trellis systems that allow for upright positioning of shoots (e.g. vertical shoot positioning) 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 areas inland, 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. 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.
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, such as 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 method (i.e., spur or cane pruned), variety (some varieties do not produce fruitful basal buds and are cane pruned) and vine vigour.
In cordon-trained systems, 2-3 bud spurs should be evenly spaced along the cordon.
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.
Buds close to the cordon are basal buds and usually remain dormant. Potential crop load can be determined by sectioning buds, which 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 vigour. 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 vigour 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 vigour 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. As a rule of thumb, leave about 30 buds per kg 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.
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.
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 colour 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 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.
There are many opportunities in the life of a vineyard to adjust crop load: site selection, vine spacing, training system and pruning technique are just a few things that can influence crop load.
Vines that may be overcropped due to a small canopy size can benefit from cluster thinning to bring the vine back into balance. At least 30-40% of the crop must be removed in order to observe any differences when the fruit is harvested.
Proper timing can influence whether the benefits of cluster thinning are realized or not. The earlier thinning is practised, the larger the berries will be due to redistribution of resources in the vine. Flower thinning will allow for more open clusters in the fruit zone.
However, caution should be exercised so that fruit set is not negatively affected. Early cluster thinning after fruit set may encourage shoot growth, but can reduce bunch compactness and botrytis susceptibility. If clusters are removed at veraison, maturity can be advanced in the remaining clusters, especially if lagging clusters are removed. Finally, late cluster removal will reduce yield.
Cluster thinning should not be a long-term practice in the vineyard, and if vines are continuously overcropped, pruning and shoot thinning strategies should be revisited.
| Component | Determined during | Management options |
|---|---|---|
| Vines/acre | Planting | Density / trellis design |
| Nodes/vine | Winter pruning | Pruning level |
| Shoots/node | Budbreak - early previous season and current season | • Pruning level • Short thinning • Nutrition • Canopy management |
| Clusters/shoot | ||
| Flowers/cluster | Fruit set | • Nutrition • Canopy management • Irrigation • Nutrition |
| Berries/cluster | ||
| Berry weight | All season | • Irrigation • Nutrition • Crop thinning |
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 vigour and development of the root system, maintaining the vine shape while replacing injured or warn out areas. Goals are to:
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 vigour 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, but only two methods of pruning. These differ in the length of one-year-old wood retained after pruning:
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 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.
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. If it's 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 is restricted to vines which are cordon trained. Spurs consist of 1-2 buds, not including the very basal bud. Two to three 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 overcrop 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.
Canopies that are overly vegetative and large can reduce air flow, 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 that 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.
If hedging is done midway through fruit development, the lag phase, then the vine has a better chance of developing those newly developed leaves to produce sugars rather than later in the season. 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.
In vineyards where there is excess vigour or lateral growth, leaf removal can be practised 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) either by hand or mechanical means. Leaf removal can be employed to get better light exposure and air movement into the fruit zone.
Excess removal of leaves around the fruiting zone, however, may delay ripening and reduce sugar accumulation and also leave clusters open to sunburn.
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, such as in the Interior, timing of leaf removal has been shown to not affect yield components or fruit composition.
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.
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.
Based on a number of recommendations by Richard Smart, the ideal canopy can be defined by a number of characteristics:
Although these recommendations are a good guide, be sure to take into consideration your vineyard site, grape variety and vigour 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 should be to have the proper balance of vegetative and reproductive growth to optimize fruit quality and yield.
In summary, 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.
