Wine Openers

VinCo, the annual Colorado wine-industry tradeshow and conference sponsored by the Colorado Association for Viticulture and Enology (CAVE), kicks off Monday (Jan. 16) and of certain interest will be the discovery of Phylloxera in commercial vineyards in Colorado.

The bumps on the underside of this grape leaf are caused by Phylloxera. A strain of the insect that attacks the roots of vines is found in Colorado. Photo courtesy Univ. Of Wisconsin-Madison

Phylloxera, as any good student of wine should know, is a microscopic aphid which, depending on the strain, feeds on the sap in grape vine leaves or roots. The aphid causes fungal infections as well as galls (see photo taken by researchers at the University of Wisconsin-Madison) to grow around the feeding site, blocking the flow of nutrients to the rest of the vine and potentially killing the vine.

Certain varieties of grapes, particularly the much-preferred European (Vitis vinifera) grapes, are extremely susceptive to Phylloxera while some native American grapes, which developed alongside Phylloxera, are tolerant or resistant. In the 1850s Phylloxera inadvertently was transmitted via infected grape vines to Europe and by the late 1860s the louse was making havoc of the European vineyards, especially in France.

It’s estimated that nearly three-quarters or more of Europe’s vineyards were stung by Phylloxera. Not until European growers learned to graft European vines to aphid-resistant American rootstock did Europe’s wine industry recover.

Phylloxera has been seen in wild Colorado grapes for years but not until in 2015 was it found in a commercial vineyard on the Front Range and then last November on the Western Slope.

“I’ve been concerned about it for quite some time,” said Bob Hammon, an extension agent with the Colorado State University Extension in Grand Junction. He said records of Phylloxera in Colorado go back at least a decade or more. “I figured it was going to catch up with us eventually.”

Because it was thought Colorado vineyards were Phylloxera free, grapevines here mostly are own-rooted, not grafted roots. The benefit is that should the vines freeze to the ground (which happened here in 2009, 2013 and 2014), the new growth will be true to the variety planted.

With a grafted root, if the upper part freezes, you don’t know what will sprout below the graft.

Grafting popular European grape varieties to American rootstock doesn’t get rid of the aphid but you get the grapes you want. Because Phylloxera is spread through the soil, one way to prevent spreading the aphid when importing vines is to hand-dip each vine in hot (125-degrees or so) water.

John Behr and Nancy Janes of Whitewater Hill Vineyards and Winery started hand-dipping several years ago when they began importing rootstock from Phylloxera areas in the eastern U.S.

“Back there, hand-dipping is an accepted practice,” Nancy Janes said. “When we’re getting grapes from known Phylloxera areas, we do it as standard practice.”

That includes parts of both California and Oregon, popular rootstock sources for Colorado’s grape growers.

Although other wine-producing areas have spent many years and even more dollars studying Phylloxera, research in using grafted rootstock is sparse in Colorado, said state viticulturist Horst Caspari.

“We haven’t had that necessity,” he said. “But the rest of the world uses grafted rootstock and we can build on that.”

Because Phylloxera kills slowly, Caspari said grape growers have time to adapt to new methods of vine management.

One current option calls for uprooting and burning infected vines and the field left fallow for a year before replanting grafted rootstock. But grapes need three years to produce a crop and that’s four years in all, “a long time to be without a paycheck,” noted Hammon.

Also, since Phylloxera can be spread on dirt-covered farm equipment, vehicles, and even vineyard clippings, management becomes more complex, said Hammon.

“We have to extra diligent about sanitation, paying attention to how you move equipment and people from field to field, it’s very challenging,” he said.

And wine-making already has its share of challenges, Nancy Janes noted.

“It’s absolutely heart-breaking knowing that it’s here,” she said.

The VinCo panel discussion on Phylloxera will be 1 p.m. to 5 p.m. Monday at Two Rivers Convention Center. Information at the CAVE website.