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Grapevine virus research in South Africa has been strategically reorganised into a single programme with a view to dramatically decrease its incidence and spread. The rapid spread of grapevine virus diseases, particularly leafroll, is a source of concern to the South African wine industry.
This emerged from a statement by Winetech (the Wine Industry Network for Expertise and Technology), following increasing reports on leafroll in South Africa in the foreign press - reports slated by Winetech as negative, exaggerated and containing quotes that are out of context. In one report the extent of leafroll spread has been given as up to half of the country's vineyards, but the industry experts insist that there are no reliable statistics available.
"Measures to combat the disease have been stepped up considerably and it is believed that a sound foundation has been laid which should dramatically decrease its incidence and spread in the next five years," according to Winetech. Meanwhile, because of a definite spread of and growing attention to leafroll, the spending on virus related research, funded by the South African Wine Industry Trust, has been increased from R6,5 million in recent years to R10 million in the next five years.
The problem lies in that it delays grape ripening and, depending on the level of infestation, reduced crop yields and vineyard lifespan.
It is also believed that an acute awareness of this "old problem" has been brought about by the restructuring of the industry in recent years, with a growing international focus and absolute emphasis on quality. At the same time, there has been a significant swing towards the planting of red grapes, in which the virus infestation is more easily observed because of the distinctive red colouring of the leaves.
Winetech recently invited a leading international expert, Dr René Sforza, from Montpellier in France, to visit South Africa to evaluate its programme and give advice. Dr Sforza, an entomologist at the European Biological Control Laboratory (USDA-ARS), concluded that a step by step replacement of vineyards with clean plant material, together with the active control of vectors (mealybug) could have a dramatic "shrinking effect" on the leafroll problem in South African vineyards within the next five years.
According to Dr Sforza, the South African research efforts are focused and moving in the right direction. But he reported noticing "a lack of communication between researchers, plant improvement organisations and producers", as reported in the technical section (Wynboer) of this magazine in August under the title "Leafroll Research In South Africa: French expert's impressions".
"Producers in particular should be regularly informed about progress with the research effort and field days should be arranged to highlight aspects surrounding the virus problem. Consultants should provide a link between researchers and producers. The negative effect of viruses on wine quality should also receive special emphasis."
The reorganised virus programme is under the leadership of Dr Johan Burger of the University of Stellenbosch, who said in a recently published paper (WineLand/Wynboer July 2001) that grapevine viruses had grown in stature in the past two decades and are today some of the most important diseases (in the case of grapevine leafroll disease) affecting the vineyards of the Western Cape.
"One of the most worrying aspects of this disease is its rapid rate of spread, better known as 'the re-infection problem'. It is estimated that - in the presence of the vector and a virus source vineyard - a newly established vineyard can become completely infected in a few years. These levels of infection have harmful influences on both fruit quality and yield, and contribute significantly to the relative short lifespan of our vineyards."
Several research projects to counter virus diseases had been initiated over the years, said Dr Burger, but these did not make any significant progress towards solving the problem. Although most existing research projects would continue, it was decided that the research effort should be directed in a few focus areas*.
Winetech's advisory committee - representing all role players concerned - has identified grapevine leafroll disease as the top research priority with a view to finding a lasting solution to the disease.
Meanwhile, all role players in the SA wine industry are represented on the Board of the Vine Improvement Association, who administers the "SA Certification Scheme for Wine Grapes", aimed at preventing problems like leafroll.
A new generation of winegrowers is leading the way with viticultural advancements, with specific care taken in new plantings. In order to prevent transition of the virus, rootstock and new material is checked, tracing the viticultural lineage. Farming implements are handled with care and known vectors of the virus (mealybug) are isolated with proper management. Virus infected vineyards with a viable lifespan ahead of them, are managed scientifically in order to minimise the occurrence of unripe phenolics with appropriate stress management. Accordingly, allowance has been made in South Africa's Integrated Production of Wine programme to allow for more spraying of mother blocks for mealybug, but still adhering to the prescribed abstinence periods.
Because of new quality standards and market trends, South African vineyards are undergoing a rapid replanting process - 38% of its vineyards have been replaced in the past seven years and 20% of them are four years old and less, 80% is red, and, according to Winetech, the majority of this being free of harmful viruses.
Regular International Awards appear to prove that leafroll does not jeopardise the country's premium wine development. In fact, UK wine expert Robert Joseph said recently at a tasting of South African red blends that "the reds have genuinely come of age in the new millennium". He felt that the elimination of many of the virus problems, as well as other improvements in viticulture and cellaring was bearing fruit and was very encouraged by this.
Commenting on the dramatic decrease in the hectarage of vines for red grapes of 16 - 20 years old - from 1 707 - 850 hectares in the past five years - blamed on leafroll virus in a British press report - the Executive Director of Winetech, Jan Booysen, said it could only be a structural change, probably mostly because of Cinsaut, previously important for brandy production, being uprooted in favour of more upmarket varietals. At the same time red grape vineyards older than 20 years, still represent 4 700 hectares, compared with 5 069 in 1996.
* The research focus areas are:
- Cassie du Plessis
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Photo right: The root of all evil... vine mealybug, Planococcus ficus.
He added that the multi-disciplinary approach of the research projects was particularly important to control this problem. Plant improvement organisations should collaborate to limit infection. He confirmed that it is caused by the transfer of viruses by means of scale insects, with vineyard mealybug being a recognised vector of the so-called "leafroll 1", while the longtail mealybug, Pseudococcus longispinus, is a vector of "leafroll 3".
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