Economic losses from Grapevine leafroll-associated virus 3 total tens of millions of dollars in New Zealand alone, a country that accounts for 0.9% of world wine production.
The virus is transmitted by insects called mealybugs which spread it while feeding on grapevines.
Leafroll 3 reduces grapes’ sugar content, flavour, and yields – particularly for premium red-grape varieties such as Pinot Noir.
There is no cure for leafroll 3 and, once infected, vines eventually succumb to the disease leaving growers with no option but to remove them and replant entire vineyards at considerable expense.
Bell, a scientist at Plant & Food Research in Havelock North, has shown the virus can be accurately diagnosed by visual assessment on red varieties.
Growers can then remove individual infected vines annually – a process known as roguing.
The research also demonstrated that only infected vines need to be removed, not the healthy nearest neighbouring vines as well, as was previously assumed.
In addition, Bell’s work has added much-needed clarity to the relationship between the disease and the mealybugs that carry it.
“The complete elimination of mealybugs from vineyards is not needed and would probably be impossible, but to control the virus we do need low population densities of vectors.
“So growers must not only manage their infected vines but also the mealybug populations in their vineyards.”
Bell’s doctoral research is supported by NZ Winegrowers, the national wine industry organisation, and Plant & Food Research.
'So growers must not only manage their infected vines but also the mealybug populations in their vineyards.'
His supervisors, Professor Phil Lester from Victoria University and Professor Gerhard Pietersen from Pretoria University, South Africa, said his work was significant and demonstrated the value of dedicated scientific research for NZ wine and viticulture.
For the past five years Bell has been a key team member of a NZ Winegrowers’ project that is tackling both leafroll 3 and mealybugs in participating vineyards.
The project, co-funded by the Ministry for Primary Industries’ Sustainable Farming Fund, extended over Hawke’s Bay, Wairarapa, and Marlborough.
Using protocols that incorporated findings from Bell’s research, many vineyard managers had been able to reduce disease incidence to less than 1%, improving the longevity and economic viability of their vineyards.
“Vaughn’s work has helped halt the spread of leafroll 3 within NZ vineyards,” NZ Winegrowers research general manager Dr Simon Hooker said.
“His ongoing engagement with the sector has also helped generate greater awareness among growers about the disease and the role played by mealybugs.”
Bell said his work on finding ways to reduce the impact of leafroll 3 was far from over.
“We've developed what seems to be an effective virus management programme in red-grape varieties.
“The next challenge is to do the same for the vines of white grape varieties which, when virus-infected, lack the visual symptoms.”
