Canopy Management Flashcards
Explain the aims of canopy management?
The key aims of canopy management are to:
- maximise the effectiveness of light interception by the vine canopy
- reduce the shade within the canopy
- ensure that the microclimate for the grapes is as uniform as possible so that grapes ripen evenly
- promote balance between the vegetative and reproductive functions of the vine
- arrange the vine canopy to ease mechanisation and/or manual labour
- promote air circulation through the canopy to reduce incidence of disease.
Explain canopy management and yield?
Vine organs (buds, leaves and fruit) develop in different ways when they are in shade or exposed to sunlight. In the wild, a vine needs its fruit to be exposed to the birds for propagation of its seeds. In forest conditions, it will grow until it finds sunlight (an opening in the forest canopy) and bear fruit. Therefore, in viticulture, a vine canopy that is well exposed to sunlight has positive implications for grape yields in the next growing season, promoting a greater number of inflorescences developing inside the latent bud (called bud fruitfulness).
Canopy management can also help maximise the leaf surface area that is exposed to sunlight. This increases the vine’s photosynthetic capacity (compared to a vine with a dense, shaded canopy) and means it can ripen larger yields.
Good canopy management can also influence yields (and also grape quality) by reducing fungal disease pressure. Due to poor air circulation, dense, shaded canopies dry out more slowly after rainfall or morning dew and provide suitable conditions for fungal diseases to develop. Dense canopies are also problematic when spraying fungicides, as it is more difficult to ensure the spray reaches all areas of the canopy.
Explain canopy management and quality?
The influence of canopy management in determining the exposure of the leaves and grapes to sunlight also has a positive effect on grape quality:
- increased sugar levels in grapes through greater overall photosynthesis in the vine
- increased tannin levels and greater polymerisation of those tannins, leading to less bitterness
- enhanced anthocyanin (colour) development in black grapes
- decreased malic acid – warmer grape temperatures lead to more malic acid being broken down in cellular respiration, otherwise acidity levels in the wine could be unpleasantly high (tartaric acid remains)
- increased levels of some favourable aroma precursors and aroma compounds (such as terpenes, which are responsible for many of the fruity and floral aromas in wines such as the grapey aromas found in Muscat)
- decreased methoxypyrazines, which give herbaceous characters in grape varieties such as Cabernet Sauvignon.
These processes taken together can result in fully ripened grapes with high quality potential. For example, in relation to black grapes:
- Without full ripeness, grapes would have unpleasantly high levels of acidity, harsh tannins and unripe fruit character, all of which would reduce wine quality.
- By contrast, fully ripened grapes can produce wines with a good depth of colour, ripe fruit aromas, balancing acidity and ripe tannins.
However, hot temperatures and intense sunshine on the grapes can lead to grape sunburn, which has a negative impact on grape quality and yields.
As mentioned above, canopy management can also help reduce incidence of fungal disease and therefore has implications for grape quality in this sense.
Explain canopy management and vine balance?
As well as maximising the effectiveness of light exposure within the vine canopy, one of the key aims of canopy management is to promote vine balance. Achieving a suitable balance between the vine’s vigour and crop load is essential for successful grape ripening and sustained production over future growing seasons. The optimal crop load is one that will allow the grape grower to grow the maximum yield of grapes that have the required composition for the desired wine style and quality.
Explain a vegetative cycle?
If the yield of fruit is too low (termed under-cropping) for the vigour of the vine, shoot growth continues through the vine cycle because there is not much fruit to ripen. The growing shoots and leaves compete with the grapes for sugar and other compounds needed for growth and can negatively affect grape formation and ripening. This also leads to a dense, shady canopy, and hence lower quality fruit due to lack of sunlight interception. This may also result in low yields the next year due to reduced bud fruitfulness. Low yields in the next season may lead to under-cropping in that year and hence the vine enters what is known as ‘a vegetative cycle’.
Explain a balanced cycle?
As seen in the Vine Growth Cycle, until véraison the vine’s sugars and nutrients are mainly allocated to shoot and root growth and storage. After véraison, sugars and other compounds needed for growth are mainly allocated to the fruit and shoot growth is depressed. Because shoot growth is reduced, the canopy is less likely to become dense and shady, and light exposure in the canopy is improved, leading to high quality fruit. It also results in enhanced bud fruitfulness the next year, and the balanced cycle continues.
Explain what over-cropped and under-cropped means?
Over-cropped: Used to describe a vine that is carrying more fruit than what it can theoretically ripen.
Under-cropped: Used to describe a vine that is carrying less fruit than what it can theoretically ripen.
Explain yield?
Yield is a measure of the amount of fruit produced. It can either be measured per vine (e.g. kg per vine) or over a set area (e.g. kg per hectare or tons per acre). There is a link between the yield of a vine and the quality of fruit in that a vine that is either over-cropped or under-cropped, and hence out of balance, is likely to produce fruit of lesser quality than a balanced vine. However, the yield at which the vine is balanced will depend on the natural resources of the vineyard, the planting material (plus age of vine and presence of any disease) and the wine style. Therefore, some vines will be balanced at higher yields than others.
The yield over a set area will depend on the yield per vine and the planting density. The higher the yield within a set area, the more wine can be made and sold. Therefore, even if yield per vine is low, the vines may be planted very densely to gain as much yield from the vineyard area as possible. In EU countries, legislation may specify maximum yields per set area. In these cases, if too much fruit is produced it may have to be removed when ripening or left in the vineyard at picking.
What canopy management techniques are there?
Canopy management encompasses a range of techniques that include:
- site assessment to determine the ideal grape variety, rootstock vigour, planting density and row orientation
- vine training
- winter pruning
- vine trellising
- overall plant vigour management (nitrogen fertilisation, irrigation, cover cropping etc.)
- summer pruning
- shoot removal
- shoot positioning
- pinching
- shoot trimming
- leaf removal
- crop thinning/green harvesting.
Canopy management should be a key consideration when establishing a vineyard. Choices regarding vine density will affect the vine training and trellising, and therefore these all need to be decided before vine planting. However, even with suitable training and trellising, the weather in any one year may vary and have a negative effect on flowering, fruitset or ripening. Therefore, summer pruning techniques may be necessary to adjust the balance of the vine and enhance grape ripening.
Explain vine density?
Vine density is the number of vines that are planted per hectare of vineyard. Vine densities range from as low as a few hundred vines per hectare to over 10 000 per hectare.
Vine density will influence within-row spacing and the between-row spacing of the vines, and therefore needs to be considered during vineyard establishment.
The optimum vine density is influenced by the vigour of the vine (which in turn is influenced by natural resources and planting materials), the type of trellising system used and what access is needed between the vines. Vines that are low in vigour and VSP trained can be planted very closely together within the row as the individual vines are relatively small.
Planting the vines with greater within-row spacing would not maximise the vineyard land (leaving gaps in the canopy within the vine rows), particularly important on expensive land such as Grand Cru Burgundy vineyards.
By comparison, vines that are high in vigour will need greater within-row spacing to grow and be in balance. Planting these vines too close together could lead to overlapping canopies and increased shading, reducing ripeness and quality.
Vines grown in dry regions without irrigation may also be planted at low density, despite not being large in size, so that the roots can spread out (without competition from other vines) in search for as much water as possible.
Between-row spacing also needs to be considered. Vine rows should be planted far enough apart so that one row does not shade the next. Therefore, vigorous vines that are high-trained and trellised need greater spacing between the rows. The width of any machinery that might be used also needs to be considered when planning between-row spacing.
Overall, low density, widely spaced trellised vineyards are usually cheaper to establish and maintain than high density, tightly spaced vineyards, requiring less planting material and permitting easier mechanisation.
Explain the choices of row orientation?
Row orientation will depend on both climatic and logistical factors. It is generally considered that a north-south orientation provides the most even sunlight exposure through the canopy. However, because conditions in the afternoon are usually warmer than those in the morning, grape bunches on the west side of the canopy (which are exposed to the afternoon sun) may require more shading from leaves to protect them from sunburn.
Prevailing winds may also be a factor in decisions on row orientation, with grape growers choosing to orient the rows at a 90° angle to the direction of the wind to provide most protection.
From a logistical standpoint, orienting rows parallel to the longest side of the vineyard is often the most efficient option. Vineyards on slopes at an angle of greater than 10% need to be planted up and down the slope rather than across or machinery may slip (unless the vineyard is terraced).
The most appropriate training and trellising method depends on what?
The optimum method of vine training must be decided at vineyard establishment.
The most appropriate training and trellising method will depend on:
- The vigour of the vine – Vigour depends on the natural resources available to the vine (particularly temperature, water and nutrients), the planting material (grape variety, clone, rootstock) and the presence of any disease (e.g. viruses can lower vigour); note that humans can have an influence on the natural resources available (e.g. vine vigour can be reduced by purposely limiting water availability in regulated deficit irrigation or by using low-vigour rootstocks).
- The topography of the site – Many trellising systems cannot be used on steep slopes or windy sites.
- The need for mechanisation – Certain training and trellising systems are more suited to mechanisation than others.
Explain vine training?
Vine training typically refers to the shape of the permanent wood of the vine and can be split broadly into two categories: head training or cordon training. Either system can be low-trained (the vine trunk is short), to benefit from heat retained by the soil or provide greater protection from wind, or high-trained (the vine trunk is long), to better avoid frosts or make manual interventions, such as harvesting, easier. Some trellising systems are only possible with relatively high training.
Head training – These vines have relatively little permanent wood. The permanent wood usually consists of the trunk, sometimes with a few short stubs growing from the top of the trunk. They can either be spur-pruned or replacement cane-pruned.
Cordon training – These vines typically have a trunk and one or more permanent horizontal arms of permanent wood, typically called ‘cordons’. They are usually spur-pruned. Cordon training takes longer to establish than head training due to the amount of permanent wood.
Explain vine pruning?
Pruning is the removal of unwanted parts of the vine. It takes place in the winter and summer. Winter pruning is particularly important as it determines the number and location of buds that will form shoots in the coming growing season.
There are two types of winter pruning:
Spur pruning – Spurs are short sections of one-year-old wood (the shoots from the last growing season that have lignified) that have been cut back to only two or three buds. Spurs can either be distributed along a cordon (cordon training) or around the top of the trunk (head training). Spur pruning is easier to carry out than replacement cane pruning and can often be mechanised.
Replacement cane pruning – Canes are longer sections of one-year-old wood and can have anything between 8 and 20 buds. They are typically laid down horizontally and need tying to a trellis for support and positioning. Replacement cane pruning is more complex than spur pruning and requires a skilled labour force to pick suitable canes and train them.
The number of buds left on the vine will depend on the vigour of the vine, with more buds left on for more vigorous vines. This in turn influences the number and size of shoots in the growing season and the amount of fruit, thus greatly influencing the balance of the vine. There are various techniques grape growers can use to determine how vigorous the vine is and how many buds need to be retained to keep the vine in its balanced cycle.
What is trellising?
Trellises are permanent structures of posts and wires that help to support and position the vine’s shoots. The vine’s tendrils will naturally curl around the trellis wires and help keep the canopy in place. The grape grower will also tie in branches and shoots to the trellis as necessary.
