Study: Grafting does not harm Washington winegrape quality

PROSSER, Wash. -- After years of research, Washington State University scientists say grafting does not reduce the quality of the state's winegrapes.

Washington is unusual among the world's major wine regions for growing its grapes on variety vines not grafted onto rootstock.

Other regions graft to avoid phylloxera -- a tiny sap-sucking insect -- and nematodes -- microscopic worms that can attack vine roots. Those problems have not yet reached Washington vineyards but growers are concerned they might. They're concerned quality might suffer if they graft varieties onto rootstock.

WSU researchers, led by viticulturist Markus Keller, just completed a project their predecessors began in 1999. Results were published in the March issue of the American Journal of Enology and Viticulture.

"The short answer is don't be afraid," said Keller, who works at the WSU Irrigated Agriculture Research and Extension Center in Prosser.

WSU enologist Jim Harbertson, also at the center, agreed, saying, "What we saw is that for all practical purposes there is no difference."

Climate, not absence of rootstock, is responsible for Washington's high-quality grapes, Keller said.

Water deficit overrides any vigor-promoting influence a rootstock might exert in wetter climates, he said. Growers will be able to continue using vineyard management techniques they've already mastered even if growing grafted vines, he said.

Beside climate, scion, vineyard location and vintage are driving factors of grape and wine quality, Keller and Harbertson said.

Over time, nematodes will build up in soil and second- or third-generation vineyard plantings probably will need to be grafted, Keller said. But right now it's better to stay with own-rooted plants for probable better recovery from freezes and to avoid grafting costs, he said.

-- Dan Wheat

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