Wine industry hailed for virus control

A South African professor specialising in plant research has congratulated the New Zealand wine industry for executing a world-first in developing an innovative strategy to deal with leafroll virus in vineyards.

Vines infected by leafroll virus turn a reddish purple colour before their leaves roll down, producing smaller fruit clusters and a lower brix (sugar level) at harvest.

The disease does not kill the vine, but it can be spread by infected nursery stock or mealybugs.

Speaking at the Romeo Bragato conference held in Blenheim last week, University of Pretoria ARC-Plant Protection Research Institute professor Gerhard Pietersen credited the New Zealand wine industry for its work on leafroll indicator grafting to visually identify the virus in white varieties, which did not display the same clear symptoms as red varieties.

The grafting trial, which took place last spring at a Hawke's Bay Mission Estate vineyard, involved taking the bud of a red variety, grafting a T-bar into the vine of a white variety, and inserting the bud to see whether it was infected.

Mr Pietersen emphasised the importance of leafroll virus management, which had helped contain the disease in red varieties in many South African vineyards.

Early intervention was vital to minimise the impact of the virus, he said. This included monitoring vines for symptoms and roguing or removing infected vines to prevent the virus spreading.

A premium South African wine label had reduced the number of infected vines and roots in one vineyard from 957 in 2003 to 17 this year by roguing.

"If you find there are a couple of leaf rolls in your vineyard, get in, remove them - don't take the risk," Mr Pietersen said.

Hawke's Bay Plant and Food Research scientist Vaughan Bell said low numbers of mealybugs in vineyards were crucial for disease control. The ‘first vines', or vines right next to an infected vine were the most at risk. The maximum amount of infected vines should be less than 1 per cent, he said.