The deadly (to grapevines) pest has been found in the Walla Walla Valley, one of Oregon’s premier locations. The outbreak is said to be “relatively limited,” and is believed to have spread because many growers graft grapevines onto their own roots.
The conventional practice is to graft them onto phylloxera-resident roots.
The outbreak is being blamed also on climate change. Walla Walla has traditionally had hard freezes, which slowed down phylloxera’s reproduction. “But they haven’t had a hard freeze for a while. It’s probably allowed [phylloxera] to have more generations per year, which would intensify things,” Andrew Walker, professor of viticulture at UC Davis, told Wine-Searcher, which first reported the outbreak.
“In California we can have four, five or six generations per year. In Washington they had only had one or two generations.”
The louse has an 18-stage life cycle and causes wounds on the roots, which then begin rotting.