Almost all wine grapes grown in Washington are grown on the roots they sprouted on. That’s unusual. In most of the world’s other major wine regions, grapes are grown on grafted rootstock.

That is, varietal scions (the part of the plant that produces the leaves, buds and fruit) are grafted onto rootstocks resistant to phylloxera - a tiny sap-sucking insect - and nematodes - microscopic worms that may attack the roots of vines. For a variety of reasons - mostly unknown - Washington vineyards have not yet been plagued with phylloxera and nematodes.

The operative word is yet. The specter of a vine-destroying invasion has lurked in the shadows of Washington vineyards for years. What if, wine industry professionals have fretted, growers had to start grafting in order to beat the insects and worms?

Would grafting affect wine quality? Are Washington wines great in part because their grapes grow on own-rooted vines?

No difference detected

Answers to those questions have been years in coming and have required a monumental, multi-year effort on the part of Washington State University researchers. A team of scientists led by WSU viticulturist Markus Keller just completed a project that their predecessors began in 1999, with results published in a pair of papers in the March issue of the American Journal of Enology and Viticulture.

"The short answer,” said Keller, the Chateau Ste. Michelle Professor of Viticulture based at WSU’s Irrigated Agriculture Research and Extension Center in Prosser, "is don’t be afraid.”

Enologist Jim Harbertson, also based at the Prosser station and a cooperator in the study, agreed.

"The big push back against grafted rootstocks in Washington has been the fear that wine quality won’t be as good. But what we saw is that, for all practical purposes, there is no difference.”