Leaf roll, mealy bugs and more to come

Liz Sagues discovers the fascinating world of leaf roll virus and what Nic van Aarde, winemaker at Oldenburg Estate in Stellenbosch, and his colleagues are doing to combat it in a recent Let’s talk about… session. She also looks forward at what’s to come in 2024, and highlights some gems from 2023.

The Circle’s penultimate online presentation in 2023 answered a question that has long puzzled many of us: is leaf roll virus the cause of the smoky, tarry taint sometimes identified in South African red wines?

No, said Nic van Aarde, winemaker at Oldenburg Estate in Stellenbosch. Instead, he pointed to research from Stellenbosch University which linked the problem to the use of vine support poles treated with a tar-based preservative. Fruit from vines close to the poles showed taint, and the level decreased the further the vines were from the poles.

Those poles are no longer used, Nic continued. With ‘green’, differently treated poles the taint vanished. But the leaf roll virus continues its insidious harm.

The measures at Oldenburg to eradicate the virus from its vines were enlightening – and, for South Africa and the wider wine world – a frightening challenge. The spread of the virus, which significantly affects the overall health of older vines, the full phenolic ripening of grapes and the quality of must, is down to mealy bugs. Yes, another sap-sucking insect, though not yet as damaging as phylloxera. There is, Nic emphasised, no cure for the virus itself – and its vector bugs are very, very difficult to control. “We are in it for the long term,” he warned.

South Africa is not the only wine country affected, he continued. Australia and New Zealand are among others that suffer, though in the latter growers in Hawkes Bay, with government help, have been pretty successful in stopping it. 

At Oldenburg, initial control efforts involved drenching affected vines in insecticide to kill off mealy bugs. But more environmentally friendly recent methods have been to introduce ladybirds and parasitic wasps into the vineyards, to hunt down and destroy the bugs. After five to six years’ effort, Oldenburg is winning – but this is helped by the remoteness of its Banghoek Valley site and the ongoing effort to identify and remove every affected vine, roots included.

Nic van Aarde in his state-of-the-art winery

The detail of Nic’s fight against leaf roll virus, as well as the background story of a winery ‘in a beautiful little piece of heaven’ where quality is paramount, is in the recording of the Challenges in Stellenbosch session (November 21), available through the Circle website members’ area.

There have been other cracking sessions in the autumn 2023 Let’s talk about… programme, including Florence Tilkens Zotiades linking Greek wine ancient and modern, the delights of cru Beaujolais explained by Cameron Jones and a description of the important educational role of the Barolo & Barbaresco Academy from Sandro Minella.  Links to recordings of them all are on the website.

Looking ahead into the new year, subjects will include the future of ice wine in the climate crisis, different aspects of the current efforts to preserve and celebrate old vines and tours through important wine regions.

Main image: The spectacular setting of Oldenburg Vineyards in the mountain-girt Banghoek Valley