Economic losses from Grapevine leafroll-associated virus 3 total tens of millions of dollars each year in New Zealand alone.
The virus is transmitted by insects called mealybugs, which spread the disease 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 the virus 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.
But now Vaughn Bell, a scientist with the New Zealand Institute for Plant & Food Research, has shown that 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 has 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,” said Bell. “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.”
For the past five years, Bell has been a key team member of a New Zealand Winegrowers’ project that is tackling both leafroll 3 and mealybugs in participating vineyards.
The project extends over Hawke’s Bay, Wairarapa and Marlborough—all prime vinelands. Using protocols that incorporate findings from Bell’s research, many vineyard managers have been able to reduce disease incidence to less than 1%, improving the longevity and economic viability of their vineyards.
White grapes next
“Vaughn’s work has helped halt the spread of leafroll 3 within New Zealand vineyards,” says Dr Simon Hooker, research general manager at New Zealand Winegrowers.
“His ongoing engagement with the sector has also helped generate greater awareness among growers about the disease and the role played by mealybugs.”
However, Bell said his work on finding ways to reduce the impact of leafroll 3 is 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.”