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An old scourge reborn: Phylloxera attacks California grapes

California's output of grapes is forecast to fall by over 100 000 tons by 1997, victim of the first outbreak in more than a century of the dreaded insect pest Phylloxera vastatrix. The infestation could cost the premium winemaking areas of the Napa and Sonoma valleys north of San Francisco more than US$1 billion in lost income.

Production isn't expected to recover until 2002. And with replanting estimated to cost between US$18 000 and US$24 000 an acre, many of the state's smaller wineries, already hard-hit by the long U.S. recession, are not expected to survive.

The Wine Institute of California (WIC) has been quick to dismiss reports of future shortages of local wine or higher unit prices as “scaremongering.” The institute's director, Andrew Montague, called the outbreak “a limited problem now under control. “ But the California wine consultancy firm of Motto, Kryla & Fisher (MKF) believes that up to 40 per cent of the valleys' production could be threatened.

The state's scientific establishment was apparently caught unawares by a vine disorder that seemed to have long since disappeared. The last great outbreak of phylloxera was in 1878 and on the other side of the Atlantic Ocean. Rootstock imported from the United States accidentally introduced the louse into European vineyards, causing what has been called “the greatest viticultural disaster since the Flood.”

Connoisseurs still debate whether wine tasted better before or after the pest decimated vines in France and Spain.

The vines wither

Phylloxera attacks the roots of the vine, sapping fertility, reducing fruiting and, ultimately, causing it to wither. The pest reproduces very rapidly, with up to five generations every 12 months. This means the number of phylloxera can go from zero to more than a billion in a single year if conditions are right. There is no effective treatment. Because phylloxera live under the soil, pesticides slow but do not stop their advance, and there are no natural predators. Eventually, the vineyards must be replanted with new vines, which then take three years to mature.

Phylloxera cannot tolerate sand or migrate across sandy areas, which is why small pockets of original viticulture in France's Champagne region and the Douro in Portugal survived a century ago. Chile, encircled by the Atacama Desert, is the only wine-producing country in the world with no history of phylloxera infestation. Elsewhere the solution, as in the 19th century, has been to graft local grape cuttings onto the American rootstocks considered most resistant. With very few exceptions, the entire European wine industry is now a product of that Victorian ingenuity one of the first examples of systematic hybridization.

The technique produces many different rootstocks with varying resistance and differing in the yield and quality of their grapes. One is AxR1, a cross between Aramon, a variety of Vitis vinifera, and Rupestris, a native American vine. Most European vineyard owners have abandoned it, finding it insufficiently resistant for local conditions, but in California, AxR1 became the mainstay of a fast-growing industry that saw wine-grape plantings increasing by 150 per cent in the 1970s. The Oenology Department of the University of California at Davis (UCD), an internationally recognized centre of viticulture studies, gave AxR1 its recommendation, and two-thirds of all vineyards in the Napa and Sonoma valleys as well as many other of the state's wine-producing areas are planted with AxR1 rootstock.

The present phylloxera outbreak was first identified in 1983. One thousand of the region's 70 000 acres have been grubbed out so far, and 43 000 more acres planted on AxR1 will probably have to be replaced over the next few years. Fast action is needed because of the furious pace at which phylloxera travels. In the Napa Valley a century ago, it took only seven years for the louse to wipe out 20 000 acres.

But how could a rootstock, widely recognized as resistant to phylloxera in the United States, suddenly succumb to such an epidemic? Viticulturalist James Wolpert, chairman of the Phylloxera Task Force at UCD, says the answer lies in a new biotype, a Phylloxera B, which has learned to overcome the resistance of the AxR1.

A mutant appears

“Phylloxera resistance is not a black and white situation,” Wolpert says. “It is a sliding scale. What we had was a rootstock that was resistant to phylloxera here, but its resistance was not absolute. Other countries had tried AxR1, especially back at the turn of the century. In these countries, the vine was not resistant. Under our conditions, we found it to be resistant. We had tests that went back 30 years, between the 1940s and '70s, and we had no problems. As it turns out, the bugs eventually caught up with us. They mutated. Exactly how, where and when that mutation occurred we don't know.”

The main evidence for a new biotype is the current infestation and, to many, its “discovery” could be little more than a damage limitation exercise by a scientific community caught with its trousers down. Says Robert Joseph, editor and publisher of Wine magazine: “Some people say biotype B is just A with another name. I believe there is a new strain but also that AxR1 is a time bomb.”

Wolpert admits that, after a century of inactivity, the phylloxera threat slipped down the list of priorities. “It's a difficult thing to study,” he says. “We need to know a lot more about how the bug and the vine interact. It's been a worldwide situation that about the time rootstocks come onto the scene, people stop studying the bug because it's not a problem anymore. Once you've got rootstocks, people say, 'I've got more pressing problems,' and move on.”

The epidemic is sure to transform the face of the California wine industry. Annual replanting rates are predicted to rise from an average of 1 000 acres in the two valleys to 10 000 acres in 1997, according to Vic Motto of MKF, while some 30 per cent of the total wine-grape area will be out of production. With the return of phylloxera, vintners with own-rooted vines in Lake County, Mendocino, the Foothills, northern San Joaquin and along the coast between Monterey and Santa Barbara will also have to replant.

Faced with three-year profit losses and steep replanting costs, many will certainly go to the wall. But for those who withstand the crisis, the outlook could be much brighter. With closer spacing-often double the number of vines per hectare-and newer trellis systems, growers can increase production from the 1980s' average of 3.5 tons per acre to six tons and get an estimated 700 bottles of wine for each ton.

The sixty-four dollar question is what rootstock to replant in the afflicted vineyards. UCD has recommended a number of alternatives- 5C, 3309, 110R and St. George. But they may not exist in sufficient quantity to supply the wineries' needs, and their suitability for specific soils and microclimates has not been fully established. “Unfortunately, little research has been done on the alternatives,” Motto says. “Replanting decisions are being made today based on insufficient information. New combinations of rootstocks, clones and growing conditions require new research to avoid or minimize problems. Trial plantings and more funding are needed.”

The next 10 to 15 years, Motto believes, will be a resting time for the industry, which stands to lose more than 50 per cent of its premium Chardonnay supply and 90 per cent of the premium Cabernet/Merlot. AxR1, the king of California wine, is undoubtedly dead, and the search for its successor goes on.

Michael Griffin