Almost all wine grapes grown in Washington are produced on their own natural roots. That's different from most of the world's major wine areas, where vines are often grafted to another type of rootstock.
Varietal scions (the part that produces the leaves, buds and fruits) are grafted onto rootstocks resistant to phylloxera -- a tiny sap-sucking insect, and nematodes –microscopic worms that attack roots and vines.
The specter of vine-destroying invasions has lurked in the shadows of Washington vineyards for years, bringing researchers to ponder a potential shift by growers to more grafting in the state to avoid disease invasions.
The question many ask is how grafting would impact wine and vine quality.
Answers to that question have been years coming and required vast studies by Washington State University researchers. A team of scientists led by WSU Viticulturist Markus Keller have now completed a project running since 1999, with results published in a pair of papers in the March issue of "American Journal of Enology and Viticulture."
The important finding: grafting isn't affecting quality in vines or wines.
"The short answer," says Keller, "is don't be afraid."
WSU enologist Jim Halbertson agrees: "The big push back against grafted rootstocks in Washington has been the fear that wine quality won't be as good. What we saw is that, for all practical purposes, there is no difference."
Keller notes that since Washington vineyardists use deficit irrigation – apply only water actually needed by plants – to manage vine vigor, the tests also revealed no differences in vine canopy sizes.
Deficit irrigation overrides any vigor-promoting influence a rootstock might exert in wetter climates, says Keller. In other words, growers will be able to continue using the vineyard management techniques they've mastered even if they grow grafted vines.
Right now, there is really no reason to grow Washington vines on resistant rootstocks, and that saves producers money. Eventually, Keller predicts that the move to grafting may be necessary in the Evergreen State.
"Nematodes build up in the soil over time," he explains, "so increasing numbers of second and third generation vineyard plantings will likely need to be on grafted vines."