New detections of the lethal phylloxera pest in vineyards in Washington’s Walla Walla region are raising concerns about costlier management practices and potential rootstock replacements.
Over the past month, grape growers in the area have reported finding damage from the insect, which causes root galls and eventually kills the plant. The exact number of infested vineyards hasn’t yet been determined, experts say.
“It just seems to pop up in weird places on occasion. Never in Walla Walla, so that’s new,” said Katie Buckley, entomologist with the Washington State Department of Agriculture. “We’re hoping to figure out where it came from, or maybe at least how far it’s spread.”
While phylloxera affects plant vigor rather than grape quality, the Walla Walla detections are serving as a “gentle wake-up call” to refocus on clean plants and vineyards, said Vicky Scharlau, executive director of the Washington Winegrowers Association.
“There’s still great care that needs to be taken if you want a long-term sustainable vineyard,” she said.
Though phylloxera was first found in Washington grapes more than a century ago, the state’s vineyards are generally planted in sandy soils that aren’t conducive to the pest.
For that reason, growers have often been able to plant grape varieties with their own roots, rather than those grafted onto phylloxera-resistant rootstocks.
It’s possible some Washington grape producers will need to reconsider that practice as more is learned about the extent of the latest discovery of phylloxera, said Gwen Hoheisel, regional extension specialist with Washington State University.
The discovery of phylloxera is not a “catastrophe” for the region’s wine industry, though it’s an unwelcome headache at the already stressful time of grape harvest, she said. “The rest of the world has this bug.”
Grape quality and production can be maintained in affected vineyards by “pushing” vines with more water and fertilizer, though such practices cannot ward off the plant’s eventual demise forever, Hoheisel said.
The long-term solution is to replant vineyard blocks with varieties that have been grafted onto native North American grape rootstocks, which are able to tolerate phylloxera, she said.
“If you have, vineyards can stay profitable and you can manage it for quite some time,” Hoheisel said. “It’s easier to address it through rootstocks over a long period of time.”
Phylloxera proved devastating to the French wine industry in the 1800s before grafted rootstocks were identified as a solution, said Buckley of WSDA.
With many vineyards in Washington reaching 40-50 years since planting, grape growers will need to examine adopting grafted rootstocks if they’re sufficiently afflicted with the pest, she said.
“The industry here is at an age that they’re starting to replace vineyards anyway,” Buckley said.
The pest has kept a low enough profile in Washington that some grape growers were likely unaware that it’s a quarantine pest and that they’re required to buy grapevines from nurseries that have certified as being free of the insect, she said.
In sandier soils, growers may be able to continue planting self-rooted grape varieties because the pest may not be able to build up populations enough to become problematic, Buckley said. “Basically, we’re going to be doing a lot more research on this.”
It’s well known that “bootleg or suitcase plants” have come into Washington, so the situation highlights the need to be vigilant about disease, said Scharlau of the Washington Winegrowers Association.
Apart from buying certified plants, growers should control access to their vineyards, restrict vehicle travel to paved roads, avoid sharing field equipment and ensure grape bins are cleaned from soil, she said.
“This is an opportunity to talk about best management practices,” Scharlau said.