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Principles Of Organic Cultivation Of Wine Grapes*

Pieter Raath
ARC Infruitec-Nietvoorbij, Stellenbosch

Introduction

Interest in organic cultivation of wine grapes is growing world-wide. Various reasons may be suggested for this state of affairs, although the higher price sometimes paid for these products probably represents the most important motivation for wine farmers to investigate this option. Recently the growing interest in speciality wines also expanded the market for wine made from organically cultivated grapes. Wine quality is a determining factor, however, and there is pressure on producers to make high quality organic wine. In recent years there has been increased production of organic wines in Europe and quality-wise these compare very well with their conventional counterparts. If South Africa intends to occupy a significant position in the world's wine industry, South African wines that are made from organically cultivated grapes and comply with quality standards, will have to be found on the shelves of European supermarkets.

The following is a short explanation of the general principles of organic cultivation of wine grapes in order to give producers an overview of what this approach to production entails.

Definition

As a result of the confusion surrounding the significance of the term "organic", organic wine farming must first be defined. It entails the holistic production of wine grapes while increasing and improving the well-being of the agricultural ecosystem. Although some of the techniques that are applied in this instance are also to be found in the integrated production of wine (IPW), organic wine farming is different in that:

  • all synthetic inputs are prohibited, and
  • the emphasis falls on increasing the fertility of the soil.
Principles of Organic Wine Farming

Although farmers are mostly concerned about pests and fungal diseases, it is important to take note that plant protection is not the most important consideration in organic production.

Balanced plant nutrition, and the creation of environmental conditions that are optimal to the vine, form the basis of healthy plants. Consequently an organic wine farmer pays special attention to his viticultural practices. A conventional producer, on the other hand, may reduce the negative impact of poor management practices through short term inputs.

Soil management: The basis of organic production is always the soil. Soil fertility and stimulation of the soil's micro-organism populations enjoy special attention. In the conversion from conventional to organic production, the focus falls mainly on the management of the soil, in order to increase its fertility. In practice increased soil fertility and soil microbe activity are obtained by:

  • Increasing the organic matter content in the soil to the optimum, mainly by compost applications;
  • Responsible cultivation of the upper layer, including cover crop rotation;
  • Prevention of soil compaction by limiting tractor traffic and minimal use of implements.
The above practices increase soil fertility by creating favourable conditions for the microbiological breakdown of organic matter. The humus content of the soil is also increased, which improves the soil's cation exchange capacity, structure, water retention ability and aeration. The use of compost is therefore an integral part of cultivation practices. However, application of compost is not directed at plant nutrition alone. It allegedly has a positive effect on the vine's ability to offer resistance to diseases and plagues, i.e. it improves the Systemically Induced Resistance (SIR) of the vine by enriching the soil with microbiologically produced substances, such as plant growth regulators, vitamins and antibiotic substances.

The use of cover crops also plays a role in increasing soil fertility. This occurs by means of:

  • Crop rotation between grains and nitrogen binding leguminous cover crops by means of which N (nitrogen) is regularly added to the soil (Fig. 1);
  • Protection of soil moisture as a result of the mulch that has been created;
  • Increasing the soil's organic matter content by the high population of roots deriving from the cover crops;
  • Fibre from dead cover crops which acts as a source of nutrition to soil microbes; and
  • Increased water infiltration.
The sustainability of the above practices in an organic system still has to be investigated under South African conditions.


Figure 1. A nitrogen binding cover crop such as grazing vetch is cultivated in rotation with grain crops and has the ability to bind a considerable amount of nitrogen, which is made available to the vine at a later stage.

Plant protection: Although several products are available to control specific diseases and plagues, organic producers should concentrate on cultivation practices that increase the plant's SIR. This forms the basis of the strategy to curb plagues and diseases. The SIR of plants is increased by:

  • The creation of healthy, fertile soil which provides optimally in the nutritional requirements of the vine;
  • Sufficient water supply;
  • The effective suppression, and not necessarily the elimination, of plagues and diseases.

A general principle that is being followed is not to try and get rid of a disease or plague altogether, but to suppress its outbreak so that it does not take on serious economic proportions. The outbreak of a plague or disease is therefore interpreted as an imbalance which occurs in nature and which has to be rectified. The improvement of biodiversity, in order to lure predatory and parasitic insects, is used to limit the numbers of insect plagues.

However, organic producers sometimes have to spray their vineyards with natural disease and plague control products, seeing that from time to time diseases and plagues occur on a scale that may result in large losses. Organic producers are not dependent on synthetic spraying products, however, and if the climate is favourable, they spray less regularly than their conventional counterparts. Mostly they also try to use products that have the least possible impact on the environment.

Disease and plague control is not something an organic producer can afford to ignore since poor quality grapes result in poor quality wines, which, as mentioned, makes it difficult to market these wines. Downy mildew in particular remains one of the biggest problems. In Germany Hofmann (1996) found that in organically cultivated grapes, the bunches indicated a considerably bigger percentage of infection than the conventional grapes (Table 1). From Table 1 it is also clear that there are differences with regard to susceptibility to diseases between the two cultivars, with 'Riesling' in the organic system showing a much higher resistance to downy mildew than 'Kerner'. With regard to disease management, the climatic conditions in Europe are far more difficult than in South Africa. Even so, good quality organic grapes are being produced. It should therefore be much easier in South Africa.

Cultivar Year Conventional Organic
Riesling 1987 12.1 9.9
1988 1.6 2.8
1990 15.2 22.3
Kerner 1987 17.6 57.0
1988 0.0 0.6
1990 16.0 40.7
Table 1. Occurrence of downy mildew (% of bunches infected) in the cultivars Riesling and Kerner, which are cultivated organically and conventionally respectively in Germany (Hofmann, 1996).

Conclusions

Organic cultivation of wine grapes is still a novelty in South Africa and to a certain extent, shrouded in mystery. A consultant recently said such a venture requires an intrepid farmer. To a certain extent this is certainly true, since few tried and tested organic practices have been developed for South African climatic conditions and little technical advice is available. Up to now producers had to develop and evaluate their own practices, or have made use of consultants who advocate overseas practices that have not yet been evaluated in the South African context. Furthermore, a variety of so-called "organic fertiliser and plague control products", claiming to offer a solution for just about any problem under the sun, are available in South Africa. The effectiveness of many of these products has not yet been established, however, and often they are not registered for wine grapes either. The temptation is big simply to replace a conventional spraying programme with one that is organic. In the spirit of a holistic approach to production, it should be clear that this practice is not acceptable.

References

HOFMANN, U., 1996. Compared studies on organic and conventional/integrated cropping systems in viticulture. In: HENICK-KLING, T., WOLF, T.E. & HARKNESS, E.M. (EDS.). Proc. 4th Int. Symp. on Cool Climate Vitic. & Enol., 16-20 Julie 1996, Rochester, VSA. pp37-43.

RAATH, P.J., 2000. Beginsels en vereistes van organiese verbouing van wyndruiwe in die Kusstreek. In: Grondkundige Aspekte vir Optimum Wynkwaliteit in die Kusstreek, LNR Infruitec-Nietvoorbij.

* Adapted from Raath (2000).

 Wynboer is incorporated in WineLand, magazine of the SA wine producers.

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