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AERIAL GRAFTING SUCCESSFUL IN THE ORANGE RIVER VALLEY
Andrew Teubes, Voor-Groenberg Nurseries
There is a notion that aerial grafting cannot be undertaken with success in the warmer grape growing areas. This statement was proven wrong when Anstey Brothers transformed a commercial vineyard in the Douglas district by means of aerial grafting in the 1997/98 season.
Aerial grafting of a dormant winter bud onto a green shoot at the end of October/beginning of November is successfully done on vineyards in the Western Cape. There is a misconception that this is only possible in the cooler climatic regions. The contrary was proven by Anstey Brothers, who successfully transformed 6 200 vines of Fernao Pires to Ruby Cabernet in October 1997. Although temperatures are considerably higher than in the Western Cape, vigour is higher and the shoot development occurs at a rapid rate, so much so that complete development of the cordon (sometimes a problem in the Western Cape) was easily achieved during the grafting season.
The warmer grape growing areas comply with one of the most important requirements for successful transformation between cultivars by means of aerial grafting, namely above-average vigour. However, a few points should be borne in mind when aerial grafting is undertaken in the warmer areas:
Areas in the interior are often subject to late frost. The selection of a vineyard for grafting should therefore consider the probability of frost damage. For aerial grafting the vines are sawn off low, the green shoots start closer to the surface and are consequently more subject to frost damage.
Above-average vigour is often excessive. Green shoots budding out of the permanent stems sometimes develop so quickly that the attachment is fragile and easily severed. A safer alternative is not to sucker strictly to one or two shoots in the early stages, but rather to wait in order to avoid breakage (through excessive vigour) of the shoots. Certain table grape cultivars in particular are subject to this. Avoid the application of nitrogen fertiliser in the spring.
The water demand of vineyards in warmer areas is high, as much as 7 000 cubic metres of water per hectare per annum. Irrigation intervals are therefore short. A vine which is being prepared for aerial grafting demands very little irrigation and the unnecessary application of the normal quantity of irrigation water can be more detrimental than advantageous. Do bear this in mind when planning irrigation.
Be particularly careful when handling grafting material. Take all possible precautions against the buds' drying out. Always work in and out of clean water with grafting buds and budding tapes.
Protect the bud by applying a table grape bunch cover immediately after grafting (Photo 1). This ensures that the bud remains out of direct sunlight and scorching winds. The cover is removed after approximately 3-5 cm growth.
The first nitrogen fertiliser may be applied when the bud has already grown 30-40 cm. Be careful not to fertilise too soon so that a fragile attachment may be prevented. Discontinue further applications of fertiliser after the end of December, as this may result in late growth which runs the risk of dying during winter.
Growth and development in the grafting season often occur so rapidly that in the first season after grafting the crop is almost normal. Do be careful not to overload the vineyard with bearers, because this may cause permanent damage to the vine. Bear in mind that the shoot which develops on the cordon is a cane and therefore very fertile.
The above are a few of the most important points to remember when undertaking aerial grafting in the warmer climatic regions. The successes on Anstey Brothers' farm, Avoca, can only be ascribed to continued perseverance and doing the right thing at exactly the right moment in time. Inspired by the successes of their first attempt, a further 9 500 vines were transformed in the 1998/99 season. Mr Johan Jacobs, manager in charge of the project, and his vineyard team can be truly proud of their achievement.
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