Leafroll virus, which reduces vineyard yields by up to 50 percent, and delays ripening, negatively impacting on wine quality, is a major problem for both the New Zealand and South African industry,
Now, a grafting technique developed by Mission Estate’s viticulturist Caine Thompson and Professor Gerhard Pietersen from the University of Pretoria, South Africa could identify leaf roll virus in white varieties before it takes hold.
Grapevine leaf roll-associated virus 3 can be seen in red varieties, as the leaves turn red when infected. But with white varieties, it’s impossible to detect visually as there are no obvious symptoms – meaning growers often don’t realise there’s a problem until far too late.
There is no cure for leaf roll virus. The only remedy is to remove all the infected vines and replant with virus-free vines.
“The cost (net present value) of the virus where it is left untreated and the vineyard reaches 100 percent infection is approximately $57,000 per hectare for both varieties considered,” according to the Nimmo-Bell Report, published in 2006.
Professor Gerhard Pietersen from the University of Pretoria has previously written about the potential for indicator grafting to indicate the virus in white varieties, but it has never been implemented or evaluated until now.
The idea is simple: take the bud of a red variety and graft it into the trunk of white variety. If the vine becomes infected with virus then the indicator shoot, being a red variety, will express visual symptoms.
In Spring 2011, Thompson established the first field trial, in Mission Estate’s Hawke’s Bay Greenmeadows vineyard. He used Pinot Noir as the indicator shoot, grafting onto Sauvignon Blanc, Chardonnay and Pinot Gris vines.
The results of the field trial have just been released, showing the technique is a viable – and exceptionally cost-effective – way to identify leaf roll virus in white varieties.
The cost for “installation” is approximately 90 cents per vine (one off cost), with annual running costs of about 13 cents per vine (in terms of managing the shoot), which compares with a single ELISA test of $15 per vine.
“Grafting has been used for centuries in viticulture, just never for this application and use,” says Thompson. “This technique has the potential to be a real game changer for virus management in white wine varieties in New Zealand and across the world. It’s a highly cost-effective method for protecting white varieties from virus so that wine quality continues to improve as vines age.”
Further research is being carried out in collaboration with New Zealand Winegrowers, to fine-tune the technique for wider adoption. As part of this research, Mission Estate will be grafting indicator shoots on their premium white varieties in their Gimblett Gravels vineyards.
