Vineyard Scourge May Have Met Its Match

Pierce’s disease, one of the worst scourges ever to hit the U.S. wine industry, may someday be eliminated, thanks to the noodling of Richard Peterson, a winemaker with a background in chemistry.

In California alone, Pierce’s disease has wiped out thousands of acres of top-quality grapevines and threatens many more. It is ravaging hundreds of acres in the Temecula region of southern Riverside County and has already caused more than $1 million in damages there.

“Pierce’s is potentially a lot worse than phylloxera,” said Michael Mondavi, president of the Robert Mondavi Winery. Phylloxera-infected vines may be replaced on resistant roots, he noted, but that’s not an option with Pierce’s disease.

Mondavi said his winery has torn out a 70-acre block in the Stag’s Leap region that once made their best Chardonnay. “We’re thinking of planting alfalfa,” he said wryly.

If Peterson’s fix is successful, Americans soon may be buying Cajun Cabernet, Gator Riesling and Mobile Merlot. PD, as scientists call it, is one of the factors that keeps French grapevines such as Cabernet Sauvignon, Merlot and Chardonnay from being planted in southern and East Coast states, where the ailment is rampant.

“If we could wipe out PD, we could probably grow Chardonnay and Cabernet in 20 or 30 more states,” said Peterson. “I don’t see why Georgia, Louisiana and Florida couldn’t grow [French vines].”

Discovered in the last century in Southern California and originally called Anaheim’s disease, the ailment--caused by a bacterium called xyllela fastidiosa--is spread by a family of flying bugs called sharpshooters. The bacterium clogs the water-conducting interior tissue--the xylem--of affected plants. So devastating is it that at the turn of the century it wiped out more than 40,000 acres of wine vineyards in Southern California, which up to that time was the center of the state’s wine industry.

Although it’s known that antibiotics like tetracycline can kill the bacterium, until now it has been impossible to get the drug into the vines. Grapevines have an efficient mechanism for expelling foreign substances, so the first efforts to use hypodermic needles to deliver tetracycline to the plant didn’t work; the medicine leaked out. Neither did flooding the vineyard with tetracycline. The roots didn’t take up the antibiotic.

Peterson, former winemaker at Beaulieu Vineyard and the Monterey Vineyard and now the owner of Folie a Deux Winery in the Napa Valley, has come up with a low-tech solution to wiping out the bacterium.

His simple system calls for tetracycline-soaked cotton to be placed inside small, hollowed-out, open-ended nylon screws, which are then screwed into the trunk of the vine near the bottom of the plant, the head of the screw flush with the trunk of the plant to prevent leakage.

The plant’s natural uptake of nutrients extracts tetracycline from the wad of cotton and delivers it to where the xyllela is doing its damage, in leaves, grapes and interior tissue.

In 1997, after losing several vines to the disease, Peterson began experiments on Pinot Noir vines that showed symptoms of the disease on his farm in Yountville, at the south end of the Napa Valley.

Peterson, who earned his doctorate in agricultural chemistry at UC Berkeley and was technical director at E&J; Gallo from 1958 through 1968, said his tests were done in cooperation with the Environmental Protection Agency as well as with scientists at UC Davis and UC Berkeley, where Pierce’s disease has been a target of research for decades.

Two years of treatments on thousands of vines, both in California and in Mexico, have demonstrated to Peterson and some other scientists that his solution seems to have great potential for wiping out Pierce’s disease.

A.H. “Sandy” Purcell of UC Berkeley, who has published dozens of scientific articles on Pierce’s disease and various attempts to control it, said he likes Peterson’s approach.

“It’s a simple method, it’s quick and not very expensive, and the initial work is very promising,” said Purcell. “But we’re a long way from finding out if it’s really going to work. It may be a little premature to report this. We are born skeptics.

“If it works,” he added, “the real scientific labors are just starting. You have to see if it works year to year. Does it work in young vines? When do you use it? How much do you use?

“What’s so nice about it [Peterson’s technique] is that you use such small amounts of material. He’s using very minute amounts of tetracycline.” Doses that seem to work best average between 10 milligrams and 20 milligrams of tetracycline per plant.

Further testing is essential, Purcell said, to make certain that no tetracycline gets into the grapes. Among the tests yet to be conducted are those for residual tetracycline in the grapes, as well as different grapevines’ reactions to the treatment.

He said it could be two to four years before the technique is approved for use, but Peterson is pleased with his results so far. “I think we’re halfway to proving that it works,” he said. “Cabernet Sauvignon vines seem totally recovered, but it works less effectively on Pinot Noir. Clearly a lot of work remains to be done.”

He added, “I was very simplistic in my initial approach. I thought all you had to do was figure out a way to get the antibacterial agent into the vine. But the vine doesn’t necessarily fully recover. Let’s say you do kill all the bacteria. . . . That still does not repair the xylem tissue in the upper part of the vine.”

Peterson said that treating infected vines might require the cutting off of infected vine arms but that it’s much better to lose one grape crop than to lose the entire vine, along with years of production.

“You lose a year, but you haven’t lost three years or more,” he said.

Trying to control Pierce’s disease by killing the sharpshooter that spreads it has been tried. The bug loves riparian areas like riverbanks “and it’s difficult to kill all those suckers,” said Purcell. “They live along a river or a stream, and trying to use insecticides is generally illegal; if you kill a fish, you can go to jail.”

Pierce’s disease is thus more of a threat in wooded areas with streams and lakes, such as Napa, Sonoma, Mendocino and Lake counties. It has not been a major problem in the vast San Joaquin Valley, which is dry and generally free of the sharpshooter.

Also, some forms of sprays used to kill the sharpshooter have killed vines as well. Purcell said one solution has been to plant a conifer buffer zone between the source of the sharpshooters and the vines: “Sharpshooters don’t like to fly through conifer areas,” he said.

But that solution is impractical in areas such as the Napa Valley, where land is expensive and where conifers and grapes don’t often live comfortably together.

So devastating has been the ailment that a Pierce’s Disease Task Force was formed some years ago in Napa to investigate solutions.

Jack Stuart, winemaker at Silverado Vineyards and formerly on the board of the task force, said he has heard of Peterson’s work, but he isn’t ready to say it is the solution.

“Those of us who are on the task force are skeptical,” Stuart said. “Because so many instant cures have been thrown our way, we’re naturally skeptical. But his [Peterson’s] idea should be given a true scientific trial.”