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A Technical Guide for Wine Producers
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Bud break patterns in the Olifants River valley during the 2004 and 2005 seasons Part (II)
Marina Bruwer1 & Jeff Joubert2
1)WestCorp International, Vredendal
Introduction
Dormancy and the breaking/induction thereof is a complex process influenced by various factors. In a previous article prevalent climatic conditions and water shortages with an increased occurrence of salts were discussed as possible causes for budding patterns observed in the Olifants River Valley during the 2004 and 2005 seasons.
In this article the focus is on mechanical damage to vineyards and its influence on budding, as well as strategies to limit the occurrence of uneven/delayed budding.
Mechanical damage
It is likely that as much as 80% of the total crop in the Olifants River is harvested mechanically (J. Joubert, personal communication, 2006). "Green flags" were noted in certain instances during the 2004 season, where shoots were damaged and/or broken as a result of mechanical harvesting - damaged or broken shoots appear black in the middle (J. Joubert, personal communication, 2004) (Figures 1 and 2).
According to literature in Goussard (2002), the budding of long dormant buds may be the result of traumatisation, for example wounds caused by sawing off arms and straight trunks, organs being blown off and the damage of organs by implements. A possible explanation is the removal of organs that function as inhibitors to budding. Although wound hormones might play a role, and so too loss of moisture, definite physiological explanations are absent. Figures 3 and 4 show budding as a result of damage caused by mechanical harvesting.
According to Hackett and Holzapfel (2002) mechanised pruning, tipping and harvesting actions may cause damage to current growth, renewal growth and trunks. Buds are isolated as a result of vascular damage thereby impacting on spring budding, while bruised trunks lead to wound reactions that include the budding of water shoots.
The damage to leaves as a result of mechanical harvesting, be it because of wounds to arms or because of "burn damage" by juice (grape acids), may exert a significant influence on the accumulation and state of reserves in the vine and consequently budding the following spring.
Preventative strategies
Reserve levels play an important role in budding. If shoot growth continues too late in autumn, the result may be a shortage of carbohydrate reserves (Burger & Deist, 1981). The efficiency of leaves in virus infected vines, red cultivars in particular, is impaired due to the loss of chlorophyll and the blockage of vascular bundles, thus impacting negatively on the accumulation of reserves. According to Smart (2001) unbalanced vines with a shortage of reserves, for example when too many buds are left by winter pruning, may result in delayed budding and limit shoot growth in the period before flowering.
Mechanical damage may further reduce reserve levels through the stimulation of untimely budding, thereby causing the exhaustion of reserves locally. To reduce the occurrence of mechanical damage to vines, the harvesting process must be monitored carefully. The beaters form the nucleus of the harvesting chamber. Distortion of the beaters may be caused by faulty tension, resulting in abnormal patterns of movement and damage to shoots and even trellis poles (author unknown, 2004). Ground speed and beater speed (intensity) must also be taken into account to limit damage to the vine to the minimum.
Vineyard characteristics that facilitate mechanical harvesting are, inter alia, evenness throughout the entire block, with all vines having upright trunks and cordons that are firmly attached to the cordon wire. A properly developed canopy will soften the impact of mechanical harvesting (Ludvigsen, 2004). Poor vine formation practices and insufficient foliage may therefore be a contributing factor to mechanical damage to vines.
Taking into account the temperature data of a particular season, clean pruning should take place as late as practically possible. Chemical dormancy breakers may be applied in an attempt to obtain more even budding. Hydrogen cyanamide (H2CN2) (for example Dormex©) is considered the main dormancy breaker for grapes (literature in Or et al., 1999). These products influence the metabolism of the vine via the respiration system. Time of application for more even budding ranges from two to four weeks before normal budding (Archer et al., 1988; Lombard, 2003b and Wiese, 1988), and preferably within 48 hours of clean pruning taking place (J. Joubert, personal communication, 2006). The timing as well as concentration of dormancy breaker application is very important; if the application is too early, it may have no or a negative effect on the evenness of budding, while application that is too late or too concentrated may cause bud damage, which may influence the production of a vineyard (Or et al., 1999).
Blocks where cold accumulation does not readily take place, problem blocks, for example young vines that were fully developed on the cordon in the first year, blocks where the vine frame must be improved (Wiese, 1988) and cultivars such as Chardonnay with a high cold unit requirement, should receive dormancy breakers. No chemical product can serve as a substitute for cold demand, however, and some may even be phased out in future.
If premature/post-harvest budding occurs, young shoots may be removed, but bear in mind that such an action may encourage the budding of those buds that are situated in a lower position. In a certain sense premature budding (most apical bud/s on shoots) may be desirable, in view of the fact that it sustains dormancy in basal eyes. In the case of active budding and shoot growth of apical buds and especially in the presence of bunches, it should preferably be removed to minimise the exhaustion of reserves (P.G. Goussard, personal communication, 2004). If delayed budding occurs with apical domination of buds situated in a lower position, pruning may take place late in the season in an attempt to induce budding (Hackett and Holzapfel, 2002).
In a further attempt to prevent poor budding, soils should be irrigated to field capacity before budding, except in cases where deficit irrigation might possibly require otherwise (VinPro Consultation Service, 2004).
Conclusion
The accumulation of winter cold differs from year to year, with the result that the physiological stage in which the vine finds itself at any specific moment, may also differ from one year to the next. Careful planning for optimal clean pruning and dormancy breaking application dates is therefore extremely important. Logging of budding dates may be useful in planning application dates for pruning and dormancy breaking.
Vines should be managed to obtain evenness as well as balance, so that they may have sufficient reserves for the winter rest period.
Acknowledgements
Infobank, Stellenbosch University Library Service.
References
ARCHER, E. & GOUSSARD, P.G. 1988. Strategie vir bekamping van vertraagde bot by wingerd. Wynboer Tegnies. 28, 4 - 6.
BUGER, J. & DEIST, J. 1981. Wingerdbou in Suid-Afrika. Second reprint. CTP Boekdrukkers, Cape Town. pp. 219 - 220, 242, 530.
GOUSSARD, P.G. 2002. Dormansie. Viticulture and Oenology Department, Stellenbosch University. p. 95.
HACKETT, S. & HOLZAPFEL, B., 2002. Factors underlying restricted spring growth in vineyards. Australian Viticulture. 6 (5), 76 - 81.
LOMBARD, J. 2003b. Rusbreek navorsing op Sultanina tafeldruiwe. Website. http://www.dfptresearch.co.za/Table%20Grapes/Rusbreek%20-%20sultanina%20J%20Lombard.htm. 27 August 2004.
LUDVIGSEN, K. 2004. Preparing your vineyard for mechanical harvesting. The Australian & New Zealand Grapegrower & Winemaker. 480 (January 2004), 37 - 40.
OR, E., NIR, G. & VILOZNY, I. 1999. Timing of hydrogen cyanamide application to grapevine buds. Vitis. 38 (1), 1 - 6.
OUTEUR ONBEKEND. 2004. Picking rod adjustment important to fruit quality. The Australian & New Zealand Grapegrower & Winemaker. 480 (January 2004), 42.
SMART, R., 2001. Good wines stem from balanced vines. Australian & New Zealand Wine Industry Journal. 16 (3), 53 - 54.
VINPRO (SA) KONSULTASIEDIENS. 2002. Wynboer Wenke vir Maart 2002. Wynboer Tegnies. 151 (February 2002), 5.
VINPRO (SA) KONSULTASIEDIENS. 2004. Wynboer Wenke vir Augustus. Wynboer Tegnies. 181 (August 2004), 6.
WIESE, J. 1988. Verbeter stokvorm met siaanamied. Wynboer Tegnies 28 (June 1988), 4 - 5.
Summary
In the Olifants River Valley region, harvesting is predominantly mechanical. Post-harvest budding due to mechanical injury was noted. Probable reasons for the occurrence are discussed. Furthermore, general strategies for improvement of budding are mentioned.
Precise planning and execution of pruning is important. The collection of bud breaking dates could be useful. Vineyards should be balanced with sufficient reserves for even budding the following spring.
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