A new phylloxera outbreak in Australia's prestigious Yarra Valley has sparked concern over the extent of the vine-killing aphid's spread across the wine region.
Phylloxera attacks vine roots, ultimately killing the vine. European Vitis vinifera vines planted on their own roots are vulnerable; vinifera vines grafted to American vine rootstock are not. Because the symptoms are delayed, detection typically occurs some years after the initial infestation. The only sure cure is uprooting the vines and planting new ones on resistant rootstock.
The latest find came exactly two years after the discovery of phylloxera in the Foster's-owned Beavis vineyard in the Coldstream area in the center of the valley in December 2006. At that time, a "Phylloxera Infestation Zone" (PIZ) was declared and strict quarantine restrictions were placed on all vineyards within a 3-mile radius of the affected site. When further outbreaks were discovered in nearby vineyards in early 2008, Foster's immediately commenced destruction of all of the vines in the 80-acre vineyard.
The new outbreak occurred in Foster's Racecourse vineyard, about 2.5 miles from the Beavis site, and close to the edge of the original PIZ. It is believed that phylloxera spread on tractors moving between the two vineyards prior to the 2006 discovery and quarantine.
An extension of the zone was announced last week following meetings between the department of primary industries and the Yarra Valley Wine Growers Association.
At a public meeting, Dr. Tony Jordan, president of the Yarra Valley Wine Growers Association announced that, "given the experience of other areas where phylloxera has been found, on the balance of probability, there will be further outbreaks and ultimately the whole Yarra Valley will have to be declared a phylloxera zone."
The extension of the quarantine zone comes at an awkward time as the valley prepares for the start of harvest. The quarantines place restrictions on the movement of equipment and grapes into and out of the zone, creating nightmares for wineries sourcing fruit from both inside and outside of the area. As an interim measure this vintage, permits will be issued to allow grapes to be transported out of the newly declared zone under stringent regulations.
"At this time of developing weakness in the Australian wine and grape industry, and at a time of world economic recession, the increased uncertainty because of likely continuing changes to the declared phylloxera zones means some Yarra Valley wine or grape businesses will find it too hard to operate in the valley," said Jordan.
While some 70 to 80 percent of the Yarra Valley's vines are planted on non-resistant rootstock, Jordan was quick to downplay alarmist suggestions that phylloxera could wipe out the region. "The phylloxera detected in the Yarra Valley is a very slow-moving 'Type B biotype,' which only spreads by human or machine contact, so no one is expecting it to move like wildfire as it did in New Zealand or California," he explained. "Rutherglen has lived with the same phylloxera for more than a century and by enforcing strict quarantines, it has vineyards that remain phylloxera-free. We are confident that we will be able to control its spread."
The discovery has sparked concern in phylloxera-free South Australia, where the world's largest collection of old commercial vines in production is planted on non-resistant rootstock. The Phylloxera Board of South Australia last week issued a warning to growers of the risk of the aphid being brought into vineyards by tourists during the Tour Down Under cycling race.
Dudley Brown, chairman of the McLaren Vale Grape, Wine and Tourism Association, suggested that the recent phylloxera spread in the Yarra Valley increased the likelihood of it reaching South Australia, though the statistical risk of the aphid being transferred by tourists was low.