Starting from a strong foundation, The improvements in Planting material and management: Part four of five of a serialized report on old vines in South Africa

By Petri de Beer

The era of roadside vine shoot cuttings and suitcases filled with smuggled plant material is firmly in the past. In the 21st century, vineyard propagation has been fully professionalized and meticulously monitored, with exceptional care and precision applied to the cultivation of new planting material. This transformation has been a key factor in the improved health and resilience of modern South African vineyards. Now, as the first of these carefully cultivated vines enter their second decade, the industry is beginning to reap the rewards of these efforts, witnessing the tangible benefits of enhanced longevity and productivity.

In 2004, PlantSA introduced its plant improvement program for the South African wine industry, marking a significant advancement in vine material quality control. Prior to this initiative, virus detection in vine material primarily relied on visual inspections, with leafroll virus being the predominant concern—an issue that persists today. Following the program's launch, a transition occurred, leading to the availability of “three-star” certified planting material. This newly developed category, established by SACSWG, was cultivated in Foundation- and Mother-blocks situated in designated “low-risk areas,” strategically distanced from commercial grape-growing regions. These Foundation- and Mother-blocks also undergo stringent screening processes, including comprehensive mealybug and virus testing through Enzyme-Linked Immunosorbent Assay (ELISA), accompanied by enhanced monitoring measures to ensure superior quality and disease resistance.

Although no formal statistics are available on the exact number of hectares affected, Rosa Kruger, founder of the Old Vine Project, estimates that at least 70%, if not 80%, of the vineyard area in South Africa was infected with leafroll to some degree before the introduction of these new protocols. This virus compromises plant vigor, leading to uneven and fewer grape bunches and insufficient ripening. It has been cited as one of the primary reasons for the decreased life expectancy of vineyards in the past.

One of the key strategies for controlling leafroll virus implemented by the PlantSA plant improvement scheme was rigorous testing for the virus in propagation material through ELISA of not only foundation and mother blocks but also direct testing of material used for cuttings, along with traditional visual inspection techniques. As shown in (Graph 1), this vigorous testing and the positive effects observed by producers through improved plant material selection have resulted in the proportion of planting material originating from untested sources dropping from 34% in 1999 to less than 2% in 2023.

Graph 1: Percentage of vine plant material tested with ELISA for viruses in material provided to the South African wine industry for propagation (PlantSA).

The reduction in costs associated with ELISA testing for viruses and other diseases has also contributed significantly to this improvement. As of 2023, approximately 20% of vines provided to the industry were directly ELISA tested and confirmed clean plant material, a percentage expected to increase in the future. 

Starting with clean plant material, combined with an increased understanding and application of improved disease management practices, has been identified as one of the main reasons for the better performance of older vines.

The advancement and implementation of improved vineyard management protocols are intrinsically linked to developments in plant material quality. Once vines are planted though, they are exposed to a multitude of viruses and diseases present in their environment, making effective disease management crucial. Establishing vineyards with clean, certified plant material is paramount, but maintaining vine health post-planting becomes the producer's responsibility.

Disease management in vineyards falls into two primary categories: preventing the introduction of pathogens and mitigating their impact once they have infiltrated the vineyard. Controlling the microclimate plays a vital role in disease prevention; strategic measures such as windbreaks help limit the spread of airborne pests like mealybugs, which transmit leafroll virus, and reduction of humidity levels that favor fungal growth through canopy manipulation help lower disease pressure. In particular, vine wounds create entry points for wood rot diseases, making environmental control essential. A strong approach to vector management, targeting pests such as ants and mealybugs, is equally critical.

Once a disease has established itself in the vineyard, containment and eradication become the primary focus. While antiviral treatments for vineyards remain unavailable, rogueing has proven to be the most effective method for controlling viral infections that compromise vine longevity. Early detection and quarantine measures are essential in preventing the spread of disease between vineyards, alongside rigorous hygiene practices such as disinfecting equipment between vineyard sites. Although many producers perceive rogueing as an extreme measure, it remains the most effective strategy for eliminating viral infections in vineyards. The earlier it is implemented, the lower the financial burden on producers, as delayed action allows infections to spread and compound losses. Research by Hesler et al. (2022) highlights the severe impact of leafroll virus, with yield reductions of up to 35% observed in fully infected vineyards. This decline in productivity directly affects profitability, making proactive disease management essential.

Given these findings, an annual replacement of up to 6.5% of vines through rogueing has been shown to be a more economically sound approach compared to leaving infected vines in place. While some producers hesitate to remove diseased vines due to short-term costs, the long-term financial advantages of rogueing far outweigh the losses associated with viral spread. By systematically removing infected vines, producers can maintain healthier vineyards, leading to improved grape quality and more stable yields over time.

Beyond yield loss, viral infections drastically reduce vine longevity, necessitating a more aggressive replanting schedule. This accelerates production costs, requiring vineyards to invest more frequently in new plant material, labor, and infrastructure. Additionally, infected vines often exhibit weakened resistance to environmental stressors, including drought and pest infestations, further exacerbating financial strain.

Although these management practices are not new, they have been taken far more seriously in recent years due to shrinking profit margins. In the past, vineyards could tolerate the manageable yield reductions caused by diseased vines, but today, even slight losses can mean the difference between survival and financial ruin. This heightened focus on disease management across all vineyards has had a notable impact, helping older vines remain disease-free for longer. As a result, the sustained health of older vineyards may explain the higher yields observed in mature vines today compared to those of previous generations. 

These advancements and shifts in attitude towards more aggressive and integrated management practices have enabled older vines to maintain their structural integrity and resilience, allowing them to continue producing quality fruit for longer periods. The focus on disease control, particularly leafroll virus, and the implementation of rigorous plant improvement programs have collectively enhanced the longevity and productivity of South African vineyards. 

These findings highlight the critical role of PlantSA's plant improvement program in transforming vineyard health and productivity through scientific advancements and strategic disease management.