Keeping vines healthy

Leafroll virus is a destructive disease that shortens the lifespan of vineyards and lowers wine quality. Glenneis Kriel reports on ways to identify and prevent this disease.

-  Glenneis Kriel

FAST FACTS

More than 70% of South Africa's vineyards are infected with leafroll virus.

The virus negatively affects plant vigour, yields, wine quality and the productive lifespan of a vineyard.

To prevent the disease, plant virus-free plant material and manage mealybug and ant populations.

South Africa has a rich winemaking history, dating back to 1659. Even so, the country only has 4 292ha out of 89 384ha that are 35 years or older, and are recorded in the Old Vine Project.

One of the reasons for this is leafroll virus. No formal statistics are available on the number of hectares affected, but Rosa Kruger, founder of the Old Vine Project, estimates that at least 70%, if not 80% of the area under vineyards in South Africa, is to some degree infected with leafroll.

She gave more information on ways to prevent the disease during a vineyard workers development training session held earlier this year in Paarl.

THE THREAT

Leafroll virus affects plant vigour and results in uneven and fewer bunches. Yields of infected vines are at least 15% and on average 20% lower than that of healthy vines, according to Kruger. Along with this, leafroll virus affects wine quality, making it difficult to produce quality wines and in turn resulting in lower market prices. Kruger explained that the virus results in a delay in fruit ripening, uneven fruit maturity, poor sugar accumulation and colour development, especially in red varieties.

"The grape skins turn pinkish instead of its characteristic red colour," she said.

These are major setbacks, as South African farmers are either chasing high volumes to remain financially viable, or focusing on the production of smaller volumes of higher-quality wine grapes sold at better prices.