The grape phylloxera may be the stealth bomber of the insect world. The microscopic, aphid-like insect invades the world of the vineyard undetected and silently feeds on the roots of the grapes. Vines slowly wither and die, the symptoms mimicking other root disorders. The insect’s presence can be confirmed only by checking the roots of the plant.

In the eastern United States, where it is indigenous, phylloxera subsists on native grape varieties, which have developed a tolerance to it.

The insect’s destructive capacity became crystal clear when it was accidentally introduced to Europe in the mid-19th century. Phylloxera invaded wine grapes which were not resistant. By the end of the century, two-thirds of the vineyards on the continent were destroyed.

At about the same time the insect found its way to Europe, it was introduced into California as well. It now infests about 20 percent of the state’s vineyards, causing more than $1 billion in damage over the last decade.

Years before Washington became a major grape producing state, phylloxera was reported near Kennewick and on Vashon Island. Concern grew when a 1988 survey conducted by the Washington State Department of Agriculture found phylloxera in eight of 129 vineyards sampled. A follow-up survey identified another site. All but one were planted to Concord grapes. Concords are used to make juice drinks, jams and jellies.

With the survey findings in hand, Jack Watson Jr., chair of the Benton County Cooperative Extension office, organized a task force of university scientists and leaders in the grape industry to discuss options.

They decided to map the infestations and monitor any movement of the pest by traps and aerial photography. Researchers at the WSU Prosser Irrigated Agriculture Research and Extension Center embarked on a program to propagate and evaluate resistant rootstocks.

Replanting vineyards with resistant rootstock is currently the best defense. The solution is expensive, costing upwards of $30,000 per acre, and no one knows how resistant rootstocks will perform here.

“We don’t know how they will do under the cool growing conditions we have,” Watson said. “Our concern is that most of the resistant roots are invigorating. One thing we don’t want is succulent vine growth late in the season when cold temperatures could cause winter injury.”

While viticulturists have been busy evaluating plots of resistant rootstocks, Watson and the industry have been trying to get infested acreage taken out of production.

“We’ve been able to get five sites taken out so far,” Watson said. “One is a backyard find. It’s so remote that it does not represent a problem. The other three sites are in Concord vineyards in the Yakima Valley. There’s a potential problem there.”

Watson also has been keeping tabs on the insects. “I have been taking aerial photographs and aerial video of all the vineyards that are infested and all in close proximity,” Watson said.

New pictures of the same sites are taken at five-year intervals and compared. Watson looks for areas in the photographs that may indicate phylloxera has spread.

“What we have found through years of monitoring, mapping, and watching is that it hasn’t spread very much in the time it has been here,” Watson said. “We’re hoping that’s going to be the case in the future.

“If we can remove or quarantine existing infestations, the chances that it will spread under Washington growing conditions are drastically reduced. Without this diligence, I am pessimistic about containing it. I have read a lot about it and seen where in almost every place that it has occurred, it inevitably spreads.”

The stakes are big for Washington’s $100 million grape industry. Praemonitus praemunitus: forewarned is forearmed.