Plumpton Notes: Part 1

Index 1. Site Evaluation 2. Site Improvement 3. The Selection of Vine Cultivars

1. Site Evaluation

The climate of a vineyard should be evaluated on three different levels:
The macroclimate: that of the region or county. This is influenced by its: – Geographical location – Temperature summation – Dominant winds – Sunshine – Rainfall

The mesoclimate: that of the area, field or farm. This is influenced by its: – Aspect – Altitude – Wind exposure – Frost susceptibility – Proximity to seas, lakes, rivers, towns or forests.

The microclimate: that immediately around and within the plant's leaf canopy. This is influenced by its: – Row spacings – Row direction – Trellis system – Soil type and drainage – Plant management techniques

In turn, making a detailed assessment of a site's potential for growing vines will help the vine-grower to make decisions on: – The choice of cultivars grown – The pruning and training methods – Other cultural practices, such as soil management – The expected returns from the venture

1.1 The effects of vineyard macroclimate

1.1.1 Temperature

This is the major factor in determining the suitability of a region to viticulture. Sufficient heat for a sufficient length of time is required by the vine to complete its yearly growth cycle. However, most quality wines are produced in climates that are only just suitable for vine culture. This may be because slow berry ripening produces the finest tastes and aromas.

Climatic indices are useful for comparing potential and existing vineyard sites and determining which varieties are most suitable.

The most commonly used is Amerine & Winkler’s heat summation system. Amerine and Winkler (1974) found that the quality of wines produced in California reflected the heat summation of the sites on which they were produced.

The heat summation for vines is usually calculated by measuring the mean temperature for the month, subtracting 10°C (the minimum temperature for vine growth), and multiplying the result by the number of days in the month.

For example, if the average temperature for June is 15C, the heat summation for that month is: (15 – 10) x 30 days = 150 Growing Degree Days (GDD)

The heat summation for every month is then added together to obtain the heat summation for the year.

Average heat summations for major vine-growing regions are:

England has a very cool climate indeed, with heat summations averaging about 800 GDDs (Growing Degree Days), but the trend over the last 20 years has been for a significant increase.

Vine varietals can also be classified by the same sort of categories, allowing them to be matched to their appropriate areas.

There are considerable inaccuracies in the Heat Summation system:

There are other indices that can be used:

Very low winter temperatures will injure vines: freeze injury to dormant vinifera buds and wood begins at -15°C, is very serious at -20°C, and -25°C is usually fatal unless the vine is insulated by snow.

It is reckoned that a site will not be successful for vine culture if its temperature falls below minus 20°C as often as every 20 years or if the mean temperature for the coldest month is less than -1°C.

1.1.2 Sunshine

Sunshine has several effects on vine growth: – Indirect effect due to heat accumulation – Direct effect (through phytochromes) on: — Bud viability — Floral initiation — Ripening — Cane maturation

Vitis vinifera is thought to require at least 1250 hours of sunshine to produce ripe fruit. Sunshine hours decrease as you get further away from the coast, particularly the south coast, and with increased height above sea level. The amount of sunshine will also be decreased if the vineyard is close to a large town or city (by up to 10 %!) or if it is shaded by buildings, trees, hills, etc.

Sunshine hours can be measured using a Campbell-Stokes recorder. It is important to note that high sunshine and temperatures can lead to berry scorching (even in England!), particularly after leaf stripping or spray application.

1.1.3 Rainfall

Sufficient rainfall (450 – 500 mm) is necessary for the vine primarily to keep its cells from collapsing (causing wilting), which prevents them from fulfilling their vital functions. Some water stress during berry maturation may improve the quality of the crop, but severe stress is detrimental as it halts vegetative growth and causes leaf loss.

In England, drought is a problem on very young vines and in exceptional years in very shallow or free-draining sites. In fact, the availability of rainfall to the plant depends very much on the soil type and the season and rate at which it falls.

The best areas for vine-growing in England are those with low rainfall, as excess rain will:

High winter rainfall has little effect on vine growth, but some water is stored for later use. Moderate spring rain is beneficial, as it promotes shoot growth.

Some summer rain is useful, but this can encourage disease and reduce fruit set. Autumn rain is nearly always detrimental to the quality of the crop.

1.1.4 Hail

Hail can devastate a vineyard and is a serious problem in some vine-growing areas like Bordeaux. Unfortunately, hailstorms have a very localised action and are difficult to predict, so they are rarely considered when selecting a vineyard site.

1.2 The Mesoclimate

1.2.1 Aspect

Sunlight loses intensity if the angle with which it hits the ground is less than 90 degrees. This is partly because it has to travel through more air, and thus more energy is absorbed, but mostly since it spreads out over more land area. Example: A column of sunlight illuminating one hectare of land when falling perpendicularly will cover 1.5 ha if it falls at 45° and 2.5 ha if it falls at 22.5°.
A field that slopes in the direction of the sun will compensate for this to some extent, thus increasing the intensity of sunlight that it receives.

To compensate for the effect cited in the example above, the slopes should have a gradient of 45° (1:1) and 67.5° (1:2.4), respectively.

Some Rhine vineyards have a gradient of 1:2, but this is too steep for tractors to be used, so vine growing becomes very expensive.

The steeper the slope, the greater the effects of soil erosion, though other factors should be considered, such as rain intensity and the texture of the soil.

1.2.2 Altitude

The mean annual temperature decreases by 0.6°C with every 100-metre rise above sea level. This corresponds to a reduction of heat summation of around 105 degree-days a year, which makes for a later budburst and flowering and reduces the chances of the fruit achieving an acceptable level of maturity.

The generally accepted maximum limit for English vineyards is 150 metres. Altitude also increases the effects of wind exposure.

1.2.3 Topography

Slopes can be beneficial, as they:

But they can be disadvantageous:

1.2.4 Wind exposure

The dominant winds in the UK are:

Light winds can be beneficial in vineyards as they help to dry the canopy, but excess wind can have the following effects:

1.2.5 Frost susceptibility

In winter, once vines are fully dormant, they are hardy and can tolerate temperatures as low as -15°C.

However, during the growing period: -1 to -2°C destroys young shoots and inflorescences -2 to -4°C destroys all green parts and partly opened buds.

The dangerous periods are in spring and autumn: – Late spring frosts destroy the young shoots. The secondary buds will sprout, but these are less fertile and will have less time to mature. – Early autumn frosts destroy foliage prematurely and so affect the maturity of the berries and canes. Frosted berries will also shrivel up and oxidise.

There are two causes of frost: Air frosts: North winds bring air of a lower temperature than freezing. This form of frost is rare in England during the growing season.

Ground frosts: During the night, the soil and the plants lose heat by infrared radiation. On cloudy nights, this is reflected downwards by the clouds, but on clear nights, this energy dissipates into the atmosphere. If the night is still, a layer of cold air develops on the surface of the ground.

If the ground is sloping, this cold air will flow downhill as it is heavier than the cool air above it. It will continue to flow downhill until it reaches an obstacle or the valley floor, where a frost pocket will be formed. Planting vines in frost pockets is not recommended!

1.2.6 The influence of forests, seas, lakes and rivers

The close proximity of forests can be an advantageous factor as they act as windbreaks, store heat in cold weather, and reduce the effects of erosion. They can also be a disadvantage as they cool the mesoclimate in warm weather an increase its humidity. They can also harbour large flocks of birds, the most serious pests in English vineyards.

Most quality vine-growing regions are situated near a body of water, whether a sea, lake, or river. These are beneficial as they reflect the sun's rays, store heat for the autumn, moderate summer temperatures and can provide morning mists to encourage the development of 'noble rot'. However, they do increase the humidity of a site, thus increasing the risk of fungal disease, particularly powdery mildew.

1.3. Soil type

It is difficult to rationalise soils, as: – Quality is more important than quantity – Quality in wine involves individuality or typicity & so there is no absolute

Growers in traditional wine-producing countries maintain that the soil on which the vine is grown is vital to the character of the wine produced, but very little hard evidence has been brought to light to support this view.

In fact, apart from possibly the pH of the soil, no other chemical constituent has been proven to confer any particular quality to particular wines.

Vines grow successfully on a wide range of soil types as long as the rootstock is appropriate and the vine's minimal nutritional requirements are met. Fertile soils, however, are not appropriate for vine growth as they encourage vigorous vegetation that can cause problems.

The soil's structure and texture are much more important than its chemical composition. These affect its water retention and drainage properties.

Vines do not grow well on poorly drained soils as these are cooler and take longer to heat up in spring and restrict root growth leading to reduced resistance to drought and an increased risk of mineral deficiency.

Poor drainage will also reduce the bearing capacity of the soil, causing problems when passing machinery through.

To assess poor drainage, look for: – Water lying in pools on the surface for several days after heavy rain – Rushes, sedges, horsetails, tussock grass and meadowsweet – Pale green or yellow and unthrifty young plants – Blue or yellow clay subsoils or panning.

There is also common agreement that vines grow best on poor soils, as: – These restrict canopy growth (canopy management?) – They are often stony & well-drained, leading to a high thermal conductivity

2. Site Improvement

2.1 Wind protection

The effects of gale force winds are well known, but the effect of even a moderate but regular prevailing wind is less obvious and yet can result in a serious loss of yield and quality.

2.1.1 The Benefits of Shelter

2.1.2 The provision of shelter

Artificial windbreaks Advantages: – These provide instant protection – They require little maintenance – They can be mobile – No competition for nutrients and water – No harbouring of pests or diseases

Disadvantages: – Expensive – Do not last as long – Not aesthetically pleasing

Natural Windbreaks – Salix spp. (Willows) & Populus (Poplars): vigorous, best for perimeter planting – Ulnus spp. (Alders): better as internal breaks, particularly recommended are the grey or black alder. – Leylandii & Cedars: fast-growing evergreens that can become too thick

Natural windbreaks should be planted well before any vines to allow them to establish. These should be self-supporting, but if stakes are needed, they should only be one-third of the tree's height and be removed as early as possible. If allowed to sway, the resulting roots will be firmer.

Trees will need regular maintenance – weed control, fertiliser, trimming or topping and even root trimming. Care must be taken that they do not block drainage systems.

An effective windbreak slows the wind down by a filtering action. A solid block, such as a wall or hedge of Leylandii that has become too thick, will result in severe eddies and turbulence on the leeward side. This can be more damaging than the original wind. Artificial windbreaks are therefore made of small mesh netting, and trees should be of a twiggy nature without dense foliage.

A permeable windbreak can reduce the wind speed for a distance of up to 30 times the height of the windbreak. For maximum effect, the crop should be within 10 times the height. For instance, windbreaks of 8 m high should be planted every 80 m across the vineyard.

Living trees can, of course, hold pests and diseases, e.g. red spider mites & brown scale, but on the whole, they offer far more in terms of protection and beneficial predatory insects.

2.2 Frost protection

Once vines are fully dormant, they are hardy and can tolerate quite severe frost, but temperatures below – 0˚C will cause damage once the vine buds have burst.

2.2.1 Control

Site selection – This is the most effective method. Avoid frost hollows where cold air collects.

Cold air drainage – Do not create a frost pocket by planting a thick hedge or erecting a solid fence across a sloping site and thin existing hedges to allow cold air to drain away.

Height of pruning – The closer to the soil, the greater the frost risk. High wire training (e.g. Geneva Double Curtain) can raise the height of buds out of the risk of ground frost.

Delay pruning – By delaying pruning until the buds on the tips of the vines start to burst. The buds closer to the head of the vine will be slower to break, and the removal of the top growth with stimulate lower buds to develop, and these will be a week or so later.

Soil condition – Frost risk will be reduced if the soil condition is such that heat can easily be conducted from lower layers. Therefore compact, damp and weed-free soils perform best if there is a risk of frost.

Polymer coatings – Young vines can be sprayed with a polymer coating (ANTI-STRESS) that provides some insulation and protect the shoots from desiccation. The vine easily grows through the thin polymer coat.

Fans/windmills – These can mix the upper layer of warm air with the cold air layer closest to the vines (cold air sinks). Wind machines are available in two types: – Permanently installed tower mounted 1 per 15 – 20 acres
– Movable on a short tower 1 per 10 acres Generally speaking, a machine providing 10 hp/acre will effect a temperature rise of one-quarter the difference between the air temperature at 2m and that at 15m.

Heaters – Candles, burners, and braziers heat from direct radiation and convection. Effective, but can be expensive and can cause smoke nuisance.

Water sprinkling – As the water sprayed onto vine shoots freezes, it releases a little heat, ensuring that the temperature of the shoot will never fall below 0°C, even when the air temperature is as low as -9°C.

2.3 Drainage

Natural drainage ensures that water is distributed in several ways: – Runs off the surface – Taken up by plant roots – Absorbed into pores in the soil particles – Evaporates from the soil surface – Drains down through the soil

If natural drainage is insufficient for the rainfall falling on the field, then control methods are necessary.

2.3.1 Improving natural drainage

a. Improving the soil structure This can be improved by adding farmyard manure (FYM), organic matter, sand, grit and even lime to open up heavy clay soil. Therefore, it is necessary to understand the soil type of the site in question.

b. Ditches Ditches are the cheapest method of putting in artificial drainage

If the land slopes, dig a cut-off ditch across the top of the plot to intercept water from higher ground. Connect this with another ditch at the bottom of the slope.

It is important to maintain ditches and their outfalls every few years.

c. Drainage pipes Check to see if systems exist – farm records & aerial photography will show any previous drainage.

The problem may be isolated if the original system was well installed and in good condition, so try restoring: – Use divining rods to mark out. – Check ditches and outfalls – Look for patches of wetness or rust-coloured staining on the surface. – Expose pipe and rod from outlet up.

If a new system is needed: – Survey area – Draw up plans – Obtain quotes – Clean ditches

Ensure that all drainage installation is carried out when the vineyard soil is dry

Clay pipes are no longer used. Perforated plastic is now commonplace: 60 – 80 mm laterals 100, 125, 150, 250 mm for mains

Distance between drains depends on soil type. Positioning of drains depends upon the slope of the field and the occurrence of springs and wet patches.

If the slope is greater than 2% (1:50) the laterals should run across the slope. The minimum fall on laterals should be 1:250 The minimum fall on mains should be 1:400

The pipe must be surrounded by gravel (v. expensive). The depth of the fill is more important than the width. So narrow trenches are dug. For large operations, use a machine with laser depth control.

d. Mole drainage The cheap method is usually used on fields with clay subsoil (no stones). Mole ploughs have a torpedo or bullet-shaped “mole” attached to a steel coulter and form a cylindrical channel in the subsoil.

They can be mounted on the three-point linkage, on a wheeled frame or as a simple skid.

The best conditions are when the subsoil is damp enough to be plastic and form a good channel but sufficiently dry to form cracks. The field surface should be dry for a good grip and reasonably even. Dry weather after ploughing allows the surface of the bore to harden, so the effect lasts longer.

The channels should not be less than 75 mm in diameter, at least 300 mm below the soil surface, and spaced no more than 4 m apart. Some machines will fill the bore with gravel.

e. Subsoiling Subsoiling mechanically bursts the soil and artificially creates the passages which enable the free movement of water and air and allow root systems to develop fully. Subsoiling should be carried out when the subsoil is dry to obtain the maximum shattering effect.

Subsoiling in wet conditions is of little benefit and may cause further compaction. It should be carried out at right angles to any drains and should clear any drains by 75 mm to avoid damage.

3. The Selection of Vine Cultivars

Vine selection is as old as vine culture itself; for example, selecting vines with hermaphrodite flowers from the dioecious wild vines. As vine culture spread, vines were selected according to their level of adaptation to their particular environment and the types of wine required in that region.

This gave rise to the large range of varietals that we have today. Up to the nineteenth century, the selection was made by importing foreign varietals and by Mass Selection methods. Now these have been superseded by hybridisation, mutagenesis, and clonal selection.

The criteria used in vine selection are:

3.1 Methods used in Selection

3.1.1 Importing foreign varietals

This method has been very successful in the last few decades, as is shown by the world spread of varietals such as Cabernet Sauvignon and Chardonnay. This has brought out some surprising results as a cultivar's characteristics change drastically under different climatic conditions.

3.1.2 Mass selection ('Selection Massale')

This method involves passing through the vineyard before harvest and marking out those plants from which to take cuttings from. This is best done in poor years and can be carried out by eliminating plants instead of selecting them.

This method was very common but is now virtually abandoned due to the necessity to graft plants and the successes of clonal selection.

3.1.3 Clonal selection

Clones are plants originating from a single parent, which are propagated vegetatively (usually by cuttings) and, therefore, genetically identical.

The clonal selection was first carried out by Froehlich in 1896 on Sylvaner. It was almost exclusively carried out in Germany up till the 1950s but is now also done in France by ENTAV (Etablissement National pour l'Amélioration de la Viticulture) and by INRA (Institut National de la Recherche Agricole).

The criteria for selection are: – Yield; bud fertility, size of berries, coulure etc. – Sugar concentration – Must acidity – Phenolic and aroma constituents – Sensitivity to disease, drought, cold etc. – Organoleptic quality – Freedom from viral infection, esp. fan-leaf, leaf-roll, fleck, vein necrosis, corky bark, stem pitting.

The following methodology was used by J Balthazar at INRA Colmar on Savagnin Blanc in 1976:

Visual inspection of 1700 plants for virus, coulure, yield, vigour, berry colour
↓
Yield from 230 plants tested for sugar & acidity over 3 years
↓
Cuttings taken from 26 plants, grown in 7 varietal collections with 10 plants per clone over 10 years
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Virus testing- excluded 13 Micro-vinifications
↓
Only 4 clones selected

Visual symptoms are not enough for virus testing; use serological and immuno-enzymatic tests and grafting onto indicator varieties (e.g. 5BB).

To eliminate viruses, thermotherapy can be used.

The life of a clone is 30 – 40 years due to spontaneous mutation and infection, but it can be withdrawn earlier if better-performing clones are found.

There are some disadvantages in clonal selection:

3.1.4 Selection by sexual reproduction

Very little hybridisation was carried out pre-Phylloxera, as it was unnecessary. The only exception to this was the work of Bouschet (1824-1845), who crossed Aramon X Teinturier and produced Alicante Bouschet, a good quality teinturier variety.

3.1.4.1 Hybridisation

Vine hybridisation between species (interspecific hybridisation) began in the United States. The early settlers found that conditions for the culture of V. vinifera were unsuitable and grew indigenous varieties such as V. riparia, V. labrusca and V. aestivalis. The wines produced were not very palatable as they were too harsh, foxy or herbaceous. Hybrids with V. vinifera were soon developed, such as Concord, Black Hamburg and Clinton.

Interspecific hybridisation started in Europe with the development of rootstocks for grafting in the late 19th century. The problem was that V. riparia and V. rupestris are very Phylloxera resistant and graft well but have a very poor calcium tolerance. V. berlandieri has a high calcium tolerance but doesn't graft or root well from cuttings. To resolve this problem, nurserymen developed many hybrid rootstocks to cope with a wide range of soils.

The introduction of downy mildew in 1878 spurred other nurserymen to hybridise vinifera species with American ones, and many thousands of hybrids were developed. The resulting hybrids produced good yields and had some mildew resistance, but the organoleptic quality of the wine was poor.

In the late1950s, hybrids occupied 30% of the French vineyard area (400,000 ha). This led to severe overproduction problems.

Due to the poor quality of the wine produced, most areas in Europe have forbidden the production of quality wines from interspecific hybrids and only approved a small number for the production of table wines.

Nevertheless, hybrids are still used widely in Eastern USA as they have a high winter cold resistance. Although the breeding of interspecific hybrids was abandoned in France and Italy in the 1950s, in Germany, the Institute for Grapevine Breeding Geilweilerhof, among others, has been carrying on the work up until the present day. Its present aim is to develop fungus-resistant cultivars that must be grafted onto Phylloxera-resistant rootstock rather than developing a direct producer.

The most successful vines that have been developed at this institute are Phoenix, Orion and Regent.

3.1.4.2 Intraspecific vinifera crosses

These are crosses of one vinifera varietal with another.

After Bouschet came Prof. Muller from Thurgau in Switzerland. He produced the Muller Thurgau varietal by crossing Riesling and Madeleine Royale. This was a great success and presently occupies 20% of the German vineyard.

The Germans developed many other vinifera crosses at their research centres at Geisenheim, Geilweilerhof and Friburg: Scheurebe, Kerner, Reichensteiner etc.

3.1.5 Genetic modification

Some virus-resistant rootstocks have been produced but are not used in commercial vineyards.

3.2. The Choice of Vine Varietals for the English Vineyard

The choice of vine cultivars can be very confusing for the English wine producer due to the large number of varietals available and the lack of reliable data on the performance of different varietals under English conditions.

Winkler suggests there are as many as 8,000 different vine cultivars, including wild and table grapes, while Jancis Robinson lists I000 as important to today's wine drinker. Also, since 1882 when Muller-Thurgau was developed, there has been constant research by continental viticultural stations (particularly in Germany) to produce better and more productive vines varietals. To complicate the picture further, it is common to find significant differences in performance in different clones of the same varietal!

Accurate and reliable information regarding the performance of varietals in the UK is difficult to find as there are no government research stations to assist growers. Choice of a vine from its performance on the continent is not a recommendation for UK growers since the performance of vines is found to be remarkably different over here. There are also further complications, such as the effects of rootstocks, soil, meso- and microclimate etc.

3.2.1 Criteria for selecting cultivars

3.2.2 European Union legislation

The EU exercises certain controls over viticulture and viticultural techniques. There are rules concerning: – The classification of vine varieties – The classification of wine-growing areas – The prohibition on planting vines for the production of table wine – The certification of vines and propagating material – The declaration of areas for the production of propagating material.

There is a considerable effort to reduce wine legislation in the EU, and few of these controls are likely to be imposed on the UK in the foreseeable future, apart from the ban on the use of interspecific hybrids for the production of quality wine.