Containment works against viral vineyard infections
As we batten down and plan survivalin-isolation strategies with Covid-19 now a reality in SA, the recent history of wine industry pandemics is interesting.
There are two useful comparisons: the great vineyard catastrophe of the 19th century that caused the arrival of phylloxera in Europe, and SA’s perennial problem of leafroll virus. Phylloxera is an aphid endemic to the US. It dines on the roots of grape vines (mainly Vitis vinifera), the source of most of the world’s table wines.
It made its transatlantic voyage in the mid-19th century, probably in the soil of plants (including Vitis labrusca vines) imported to England from the US. It turned out to be an enthusiastic traveller. In this it was unwittingly assisted by botanists keen to share exotic plant discoveries with friends and colleagues across the Channel. By 1863 vineyards in the Rhône Valley, 1,100km from Kew Gardens, were seen to be dying from a seemingly inexplicable contagion.
It spread over the next 25 years across France and much of Europe. In 1889, wine production in France was 25% of what it had been 15 years earlier. Phylloxera was first identified in SA in a garden in Mowbray, Cape Town, in 1886. It made equally impressive progress here. By then it was also in Australia, though given the distances between wineproducing regions, its progress was slower. The Australians implemented rigorous protocols aimed at containment, wherever control was possible.
South Australia remains free of phylloxera, so it has some of the world’s oldest and most venerable vineyards. The Grandfather’s Block on the Henschke estate, planted in 1860, still contributes fruit to the cellar’s Hill of Grace Shiraz.
REGULATIONS BREACHED
Australia could for a time limit phylloxera’s spread. While parts of Victoria succumbed before the protocols were put in place, others, such as the Yarra Valley an hour’s drive north of Melbourne, survived with no evidence of the aphid for more than a century. Then, less than 20 years ago, one of the big multinationals moved farming equipment from a contaminated region to the Yarra, breaching containment regulations. By 2006, it was detected there and the Maroondah Phylloxera Infested Zone was established.
Since then the zone has been extended at least seven times, illustrating the limitations of containment as a strategy once the bug has arrived in a region carpeted with vineyards.
SA’s major vineyard problem is leaf-roll virus, an incurable infection that attacks vine leaves, turning them a lovely russet colour early in summer.
Without chlorophyll the plant battles to ripen its grapes. By late summer, the fruit is in an arrested state of development: the tannins are still hard, acidity plummets and the berries start shrivelling. Wine made from the fruit of infected vines usually shows stress characters, and is generally unsuitable for premium wines.
COST DEFERRED
The leaf-roll virus problem used to be much worse, but the protocols established by the University of Pretoria’s Prof Gerhard Pietersen (initially for growers in New Zealand with the same problem) have played a significant role in containing the spread. If individual vines manifest signs of virus they are removed, those in their immediate vicinity are marked and if necessary grubbed up.
For the cost of the loss of a few vines, transmission (either via mealy bug or contaminated secateurs) is thus arrested. Most of the vineyard therefore survives and can be nurtured towards a state of real maturity and the planting cost of R300,000 a hectare deferred.
Since the best old vines produce the most intense and complex fruit, there’s real benefit in terms of wine quality.
Containment clearly works against virus infections, and is cost-effective — unlike phylloxera for which it only takes a clod of soil in the tread of a tyre to bring about the next deluge.