A Technical Guide for Wine Producers

RECENT ARTICLES   |   WYNBOER HOME BROODKRAAL WINS WITH AERIAL GRAFTING ON ESTABLISHED ROOTSTOCKS Andrew Teubes, Voor-Groenberg Nurseries Broodkraal Estate, on the banks of the Berg River near Piketberg, overcame the current shortage of grafted table grape vines by aerial grafting (chip budding) of the desired scion cultivars onto already established rootstocks. Current shortages in grafted vines, as well as rapid switches between table grape cultivars as a result of market pressure, mean that aerial grafting offers a cost-effective alternative to the establishment of a new vineyard. The year of planting does not have to be postponed because a certain grafting combination is unavailable. By aerial grafting onto an established rootstock, it is possible to score up to two years on the choice of a scion cultivar. Broodkraal Estate did just that after shortages in grafted vines threatened to delay the development tempo of the farm. Rooted rootstocks are easily available and were established in the winter of 1997. During the first growing season, the vines were stimulated to develop as quickly and vigorously as possible, thus creating a strong vine with sufficient reserves and a strong root system. In the winter of 1998 (one year after planting) the vines were pruned back to two buds and allowed to bud from scratch. Regular suckering to one main shoot and regular topping of one or two spare shoots resulted in rapid development, the vigour of the strong root system having been channelled into a few selected shoots. Once the main shoot was substantially fixed and no longer breakable, the spare shoots were removed. The main shoot was regularly tied to a pre-strung summer shoot development rope. Thorough removal of the basis leaves and buds from the rootstock (with sharp knives) limited wind damage (due to the reduced surface of resistance) and reduced suckering, seeing that side shoots did not bud all the time. Nevertheless four to five leaves were always maintained below the growing tip. The vineyard was trained onto a pergola trellis system, with the grafting position (1,6 metres above the ground) approximately 30-40 cm below the roof. In order to support the vine, two extra wires were strung. The first was approximately 80 cm above the soil surface and the second 30 cm below the height of the roof. The developing shoot was attached at both these heights and also at the height of the trellis, in other words in three places. Consequently sufficient support was obtained and the grafting (oculation, in fact) took place about 5-8 cm below the second wire. After about 14 days the bud started to show signs of growth and was regularly tied to prevent wind damage. Further development of the permanent parts of the cordon took place as usual. Once again valuable lessons were learnt, as confirmed by Mr Oubaas Calitz, manager in charge of the successful project. The labour requirement is very high. Aerial grafting is enormously labour intensive and requires weekly attention. Preparatory work before grafting must be done promptly in order to get the vines - as many as possible and as quickly as possible - ready for grafting. Aftercare requires the same amount of attention, if not more, seeing that each graft which is lost has to be grafted all over again. Grafting material must be selected, prepared, packed and stored carefully and correctly. No effort should be spared, for if the grafting material is not handled correctly, all other steps are in vain. Moisture loss is usually the biggest danger. Stimulate the development of the rootstock as much as possible in the first growing season. The stronger the rootstock, the faster and stronger the growth in the grafting season, the earlier grafting can take place and the stronger the post-grafting development, with the subsequent advantages vis à vis crop size the following year. A weak vine before grafting will remain weak after grafting. Do not attempt to plant and graft in the same year. A vine cannot undergo optimum root development and form strong callus in the first year, regardless of the quality of the soil. Callus formation requires huge amounts of energy from the vine, which impedes root development. The result is a weak and uneven vineyard. Dedication and more dedication to the task at hand cannot be overemphasised. Success with aerial grafting is not obtained with 90% dedication - only with 100% dedication. The most important advantage of aerial grafting is probably that cultivar choices may be deferred by up to two years. In times of vine shortages and rapid switches between table grape cultivars, the selection of a suitable scion cultivar may be taken the winter before grafting (approximately 4-5 months before grafting). The first small crop of the cultivar is then harvested within a year. Two types of oculation may be done. Broodkraal used chip budding, which takes place onto a green shoot that has already lignified slightly (approximately end of October). An alternative method is split budding ("little ship"). This kind of grafting must take place on a much softer green shoot (approximately beginning of October). Both methods give satisfactory results however. The success achieved by Broodkraal Estate in the 1998/99 season was only obtained as a result of sustained attention and perseverance. Joubertsdal, sisterm farm of Broodkraal in Paarl, obtained similar results. Here the process was overseen by Mr Bernie van den Heever. Congratulations are due to both managers and their respective vineyard teams.

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