Sharpshooter to gun down the future of California wine industry
On 10 August 1999, Riverside County in southern California, home to Temecula, a fledgling but internationally unheard of wine region, declared a local emergency concerning the existence of a centimetre-long bug. A sum of $250,000 was allocated to support research.
On 23 June 2000 Al Gore, Vice-President of the USA, declared a state of federal emergency and released $22 million as part of a staggering $36.6m effort to combat what scientists and the wine industry alike are calling "the most serious ever threat to California viticulture". And the cause of this nationwide panic? - the same centimetre-long bug, Homolodisca coagulata, commonly known as the Glassy-winged Sharpshooter and a bacterium called Xylella fastidiosa or Pierce's disease.
"This is more serious than anything we've ever faced before," said one vineyard owner in the trade press this week. "The potential here is greater than anything I've ever seen. We've had Pierce's disease before, we've had phylloxera, and they were devastating, but we've never faced anything that was real that could wipe us out. You could have an industry go down here."
The problem is not the Glassy-winged Sharpshooter (GWSS) or Pierce's disease (PD) but a combination of the two. Other than being a minor pest in urban environments, the Sharpshooter itself causes relatively little direct economic damage or loss. Pierce's disease is a deadly and incurable plant bacterium that blocks the flow of sap in the vine. However, if care was taken the disease could be generally controlled, with the exception of a few hot-spots in California, because it had no effective vector - until now.
Originating from southeastern USA, the arrival of the Sharpshooter in California now gives PD the effective vector it needs to spread away from its traditional confines. A recent report on the California Department of Agriculture's website says: "A new Pierce's disease vector, the GWSS, has recently become established in California. This new vector is a serious threat to California vineyards because of its faster and longer distance movements into vineyards."
It goes on: "GWSS will spread north into the citrus belt of the Central Valley and probably will become a permanent part of various habitats throughout northern California. There is no reason to believe it will not become established along the coast and inland as far north as Mendocino County."
For a sneak preview of the potential devastation the Sharpshooter armed with PD could wreak on California you need only turn your attention back to Temecula.
"We have seen the evidence in Temecula, which was a fledgling wine region," says Steve Lyle of the California Department of Food and Agriculture (CDFA). "The bug got in there and started spreading Pierce's disease and before anyone really new what the disease meant did significant damage." Asked to quantify what significant damage meant Lyle says: "Some estimates are that in the long-term the crop may be completely destroyed by this. We are hopeful of research that could reverse this - although we don't have anything yet."
Official figures at the moment suggest that between 25% and 50% of the region's entire 3,000 acres have been lost to PD. Meanwhile research from the University of California failed to find any sampled area in Temecula free from Pierce's with anywhere from 25% to 97% of the plants infected.
In a speech to the California Assembly Agricultural Committee (CAAC) in February, leading entomologist Associate Professor Redak said: "With this level of infection and the speed at which the sharpshooter can transmit the disease, the situation in Temecula is extremely dire."
Even more worryingly, he continued: "To get a feel for how quickly Xylella diseases can destroy an industry one need only look to the now-forgotten grape industry of Anaheim. During the 1880s, Pierce's disease (transmitted by yet another sharpshooter) destroyed 40,000 acres in approximately five years."
"It was the Temecula experience that sounded the alarm," says Lyle. The risk is that the GWSS will get into the grape vines in Central Valley, Napa and Sonoma and spread PD there and do similar damage to those crops."
Signs suggest that the GWSS is on the move. By June 12, 2000, Fresno and Tulare counties had been officially designated as infested with GWSS, and eggs of the sharpshooter have been found at least once on nursery stock from the Central Valley in Napa.
But the potential for the GWSS as a dangerous vector goes beyond its ability to travel further and faster than any vector before. Indeed another characteristic of the GWSS, its feeding behaviour, may be even more serious with respect to its potential to spread the disease.
Basically the Sharpshooter feeds so low on the stem of the plant that infections that are established in the vine during summer feeding avoid being pruned out and survive the winter.
Professor Purcell speaking to the CAAC explained: "The important change that the glassy-winged sharpshooter may introduce to Pierce's disease in California is that its mid-through-late season infections made at the bases of the canes will survive the following winter."
This he goes on to explain will lead to chronic infections of PD, from where we can expect to see vine-to-vine spread of PD, which has not been the case in California before. If that occurs scientists believe the incidence of PD will increase exponentially rather than linearly, as has been the situation so far.
"The rate of increase in Pierce's disease in Temecula over the past two years suggests that vine-to-vine spread of chronic infections by the GWSS might be substantial. If this is the case we can expect explosive increases of Pierce's disease in other parts of the State that are invaded by the GWSS," said Purcell.
Some producers are putting on a brave face. However their public denial of a serious threat, might have more to do with a fear of tarnishing their brands with the word disease than what they really think. Others are more open.
"This is a greater threat than phylloxera by far," says Eric Wente of internationally renowned Wente Vineyards. "The technology exists to deal with phylloxera, at least on a basis of survivability. This is not possible at this time with the combination of the Glassy-winged Sharpshooter and Pierce's disease. The net is that, at this time, the GWSS and PD are a nasty one-two combination that appears to be unstoppable until a cure for the disease is found."
A cure is still a long way off. However with $36.6m in the pocket, there is confidence a solution can be found and a disaster averted. "The advantage now is that we see this coming, where as in Temecula we did not," says Lyle. "Right now we are in a containment strategy, the concern is the bug will escape our containment perimeters."
Research is directed towards a cure and a systemic pesticide. Aerial spraying has been ruled out, because although "anything you spray on it will kill the GWSS," according to Lyle, "these things are good flyers and will just fly a quarter of a mile away".
In the meantime a policy of "contain, contain, contain", is being followed. Some vineyards are being cleared of all nearby vegetation to rid the GWSS of natural habitats. Other vineyards are being surrounded by plants scientists believe will form a barrier to the GWSS. Most importantly all nursery stock moving from contaminated areas is being scrupulously checked for eggs.
Great expectations have been put into the discovery of a parasitic wasp discovered in Mexico that attacks the eggs of the GWSS and, "with $36m, people are confident we can contain this," says Gladys Horiuchi.
But money is not the major issue now; this has become a race against the clock. Lyle admits: "The best case scenario has us mass rearing these parasitic wasps and putting them into place at the end of the year."
Wente sums up the feeling well when he says: "The threat is large but not proven. The next several years will tell the tale."
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