So devastating is this louse that it wiped out almost the entire European wine industry in the last century. It is prohibitively difficult and expensive to treat and this time round has inevitably been dubbed the Aids of wine.
Vic Motto, a wine industry consultant, said two-thirds of the vineyards would have to be replanted this decade at a cost of more than dollars 1bn. The implications are serious for California, as the afflicted valleys produced dollars 3bn worth of wine last year, or about 40 per cent of California's premium wine.
Anthony Rose, the Independent's wine correspondent, reckons that around 26,000 acres - half of the vine land in Napa and Sonoma, both north of San Francisco - will die within a few years. The cost of replanting is on average dollars 10,000 to dollars 15,000 an acre, and that does not include lost production while the young vines mature.
According to Mr Rose: 'The massive financing required means that small growers, already feeling the pinch of recession, will find it hard to survive.'
The outbreak has its roots in history and politics and it has dented the pride of growers and wine experts alike. Phylloxera all but obliterated Europe's vineyards in the late 1800s, having been transported from North America where, ironically, the native vines are resistant to the louse. It is a strange twist of fate that has brought about the present crisis. In Europe, the vines used to make fine wine are of a type called vinifera. When phylloxera ravaged the land in the last century, inability to find a cure led growers to look to native American vines, but these could not be used to produce quality wines. The louse attacks the root, so the solution was to plant the American root, chop it off and graft on a vinifera vine.
This grafting technique can produce a variety of different rootstocks, differing in their resistance to the louse and in the yield and quality of grapes they produce. One of them is a cross between Aramon, a vinifera variety, and Rupestris, a North American variety. It is called AxR1 for short. It became the mainstay of a California wine business looking for a productive and rigorous compromise, and one that could produce premium wine.
In large plantings in the 1960s and 1970s that were the birth of the state's modern wine industry, the Californian growers opted for Axr1 for 60 to 70 per cent of plantings. They did so on the advice of researchers at the University of California at Davis and against the advice of some European experts. The Europeans believed that AxR1 gave insufficient protection against phylloxera, and it has all but been abandoned in the main European wine- growing areas. But AxR1 has the attraction of bearing large amounts of high- quality grapes and of being resistant to other diseases. So until recently, when the full horror of their situation hit the Californians, growers ignored outside advice.
The latest outbreak of phylloxera, discovered in 1983, involves a new strain, Biotype B. But there are sceptics who say that Biotype B is a scapegoat and that the difference between this and the original strain may not be to blame.
Robert Joseph, the publishing editor of Wine magazine, said: '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 . . . But the Americans are loath to admit mistakes.'
What does appear to be different is that Biotype B spreads at an alarming rate. It sucks the sap from deep in the vine roots so that they wither. One female can produce 200 offspring and the cycle of regeneration is believed to be about 30 days.
The louse has no natural predators that could help to stem its spread, and there is argument about exactly how it gets from one part of the land to another. One of the few certainties is that it dislikes sand and water. This has in the past saved small areas in Champagne in the south of France, and in Portugal's Douro, which remained phylloxera-free in Europe's infestation.
The outcome of California's plight is uncertain. Experts believe that large-scale uprooting and replanting will peak in five years and gradually taper off. But the problem does not stop there for Napa, as it is generally accepted that older vines produce finer wines. Napa, whether justifiably or not, has acquired a reputation as the state's premier fine wine area, the Bordeaux of America.
If there is a silver lining, it is that the industry will have the chance to replant with optimum varieties in terms of quality and economy. Growers say they know a great deal more about their soil and climate than they did a few decades ago. They are trying to look on current events as an opportunity rather than a tragedy.
Phil Freese, vice-president of the Robert Mondavi winery, expects the yield of the new vines to be 50 to 75 per cent higher. He says the grapes will also be better and will make higher-quality wine. At Mondavi, 700 of the 1,300 acres must be replanted at a cost of dollars 25,000 to dollars 30,000 an acre, including lost production.
The consensus is that many growers will focus on popular grape varieties such as chardonnay and cabernet sauvignon. This is unfortunate for grapes such as riesling, which are less fashionable and may be sidelined. The indigenous and much-maligned zinfandel, which can produce fine red wines but which is now used mainly for sweet 'blush' pink wines, may all but disappear.
In the nearer term, the impact for the consumer may be higher prices as replanting takes its toll on output and finances. Makers of premium wine in California already believe they are not getting enough for their produce. Recession and the trend to drinking less among the health-conscious have already led to fierce discounting.
The Wine Business Insider newsletter, published in Sonoma, reports that 18 wineries have filed for bankruptcy in as many months, while others have merged or been bought out. Robert Joseph says that about 100 wineries are believed to be up for sale.
In the short term, prices for consumers may be protected by 1991's bumper harvest. Perhaps California's producers may also find they cannot push up prices because of competition from New Zealand and Australia. Wineries in Eastern Europe are also cleaning up their act, while Western European producers are finally making positive moves to fend off the onslaught from the New World.
Whatever the aftermath of the outbreak, it has had the effect of kick-starting new research in a region that had become complacent. The growers must convince themselves that there is life after phylloxera.
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