BY Bo Simons

The fight against Pierce’s Disease (PD) in Temecula has benefitted the entire California wine industry. The scientific struggle to find information and solutions for the disease employs scores of researchers and millions of dollars all because the tiny (2,500-acre) grapegrowing community in Temecula mounted a conscious and concentrated effort to focus attention on the problem.

A look at Temecula vineyards
Driving east on Rancho California Road from Highway 15, one travels through about four miles of the boomtown known as Temecula, shiny new shopping malls alternating with crisp housing developments along a wide, pleasant thoroughfare. The sparkling new city ends abruptly at Butterfield Stage Road where Temecula wine country begins.

Temecula grapevines enjoy wider spacing than is common these days in North Coast vineyards. Some vertical trellising exists, but mostly there are lots of low, healthy vines in orderly rows among citrus groves. The sandy, tan-gray soil shows between widely spaced, lush, green vines. At mid-day, with the temperature in the mid-80s, and the air redolent of lemons, the atmosphere is serene Southern California wine country.

This does not appear to be the waste land one would expect from recent wine trade publication reports. Several reports said fall would be when the devastation wrought by Pierce’s disease would be most evident.

Where were the massive symptoms predicted? You would expect mists of sharpshooter rain wafting out of citrus groves, and exposed trellises covered with decayed, withered vines, raisined grapes beneath chlorotic and necrotic red and yellow leaves, petioles bare of leaf blades, like skeletal fingers from lignified canes.

A closer look than just driving past vineyards shows that all is not well. There are skips, rows where one, five, seven, 10 vines, or a whole row are missing. Vines sporting scorched leaves, persistent petioles, and canes with uneven wood maturation mark Pierce’s disease. Some of the enormity of the problem creeps upon you like a bad dream. The clean empty fields are not just unplanted land: they are former vineyards, ripped out.

Scars left by earth-moving equipment appear fresh upon the sandy earth. Mount Palomar Winery has the equipment pushing dirt around in the area between the winery and Rancho California Road, where both vines and citrus trees used to grow. Growers have become scrupulous about not retaining any infected vines. Pierce’s disease spreads when a sharpshooter feeds on the infected vines and then spreads the bacterial pathogen Xylella Fastidiosa that causes the disease to healthy vines.

Nature and extent of the problem
Driving up the driveway to Callaway Coastal Winery and mounting the low hill the winery sits upon, the extent of the Pierce’s disease damage becomes even more apparent. As you crest the hill, the hill beyond comes into view, where large skips are visible. To the east, whole blocks gape in silent witness where the vines have been ripped out.

Callaway’s home vineyard is among the hardest hit. The devastation lies adjacent to the Callaway tasting room parking lot, right below Allie’s at Callaway Winery restaurant.

Vineyard manager, Craig Weaver, has managed Callaway vineyard operations for 18 years. He has watched glassy-winged sharpshooters spread Pierce’s disease, and he has since helped the winery reinvent itself.

Partly in reaction to the damage wrought by PD, Callaway Vineyards & Winery has become Callaway Coastal Winery. It now sources 50% of its grapes from Santa Barbara, San Luis Obispo, and Monterey counties.

Adjacent to the Callaway Winery are home vineyards that have sustained 40% damage: about 270 of the 675 acres of grapes are gone.

Several miles away from the home vineyard lies the Bell Vineyard, owned by Callaway. Its slightly resistant varietals and distance from citrus trees make it less prone to PD. Syrah vines on SO4 rootstock are surviving, along with Chardonnay on Riesling roots next to a lemon grove.

Vines at Callaway have almost all been budded over at least once. Varietals are grafted onto varietals: Merlot on Sauvignon Blanc, Chardonnay on White Riesling, Mourvédere on Sauvignon Blanc, Dolcetto on Chenin Blanc, Nebbiolo on Chenin Blanc, Chardonnay on White Riesling.

All these changed varietals reflect changes in the winery’s marketing plans, not which varietals have the best resistance to Pierce’s disease. The different varietals grafted onto varietals make for an interesting lesson. It is the original or base vine that is the critical factor. Chenin Blanc and White Riesling are among the most tolerant.

Where Merlot is grafted onto Sauvignon Blanc, the vines are hit pretty hard, not because of the Merlot, which is fairly resistant to PD, but because it is on Sauvignon Blanc roots, which are very susceptible. The three varietal combinations that have survived surprisingly well are Dolcetto on Chenin Blanc, Nebbiolo on Chenin Blanc, and Chardonnay on White Riesling.

The vulnerability of Sauvignon Blanc and Chardonnay has been difficult, since Temecula’s reputation, and Callaway’s even more so, began with white wine. Chardonnay and Sauvignon Blanc are among the most heavily planted varieties.

Proximity to and type of citrus
Much of the research and speculation about the spread of Pierce’s disease in the Temecula area focuses on the issue of proximity to citrus. The area is one of the few in California where commercial citrus and vines co-exist. Glassy-winged sharpshooters tend to reach great numbers in the citrus, where they do little damage before moving out into adjacent vineyards where they wreak havoc.

Thomas M. Perring and others address this issue in a California Agriculture article (Perring, Thomas A.; Farrar, Charles A,; Blua, Matthew J. “Proximity to citrus influences Pierce’s disease in Temecula Valley vineyards.” July–August, 2001 Vol. 55. Number 4 Pages 13–18). Although they found some blocks of sharpshooters in the center of a vineyard and vines further from citrus more infected than those on the edge and close to the groves, generally their research indicates that infection “is most severe when the vines are adjacent to citrus, and that the damage declines as one moves away from citrus.”

Weaver adds a further practical spin on the issue. Not all citrus is equal, or equally lovely to the insects that spread PD. Glassy-winged sharpshooters prefer grapefruit and lemons. They do not find oranges, tangerines, and other varieties nearly as desirable.

Weaver points to two vineyards recently planted next to citrus groves. One next to navel oranges thrives and shows no signs of PD. The other, next to lemons, has all the symptoms and will probably have to be pulled out. “It’s the flushes,” explains Weaver. “We think the glassy-winged sharpshooter (GWSS) likes the lemon and grapefruit because they experience more growth flushes per year. During a growth flush citrus trees put out tender new wood.”

Citrus is definitely a factor in spreading the disease to vines. Glassy-winged sharpshooters, native to the Southeastern U.S., were first seen in California in 1989 in Ventura, where citrus is plentiful, but there is very little commercial viticulture. Glassy-winged sharpshooters were discovered in Temecula in 1996.

Admitting the problem,
getting everyone involved
Once the wine growing community in Temecula realized the problem, they sought consensus among themselves. Being small in acres and numbers, helped. Once the grapegrowers and wineries were united, they sought cooperation from citrus growers.

Weaver recalls Gary McMillan, who owns or manages much of the citrus in the Temecula area, including grapefruit on the northern perimeter of the Callaway home vineyard, offering to help. McMillan told Weaver, “Craig, I don’t want to be considered the guy who didn’t cooperate and help, thus leading to the demise of vineyards.”

Weaver realized that was a crucial statement because McMillan had a well-established integrated pest management (IPM) program. Any new pesticide effort could possibly affect that program. McMillan was willing to allow irrigation of his citrus groves with one 32 oz. per acre application of Admire™ as part of the program to leave Imidacloprid to kill GWSS when feeding.

The wine industry grapegrowers in Temecula realized that they were fighting not only a scientific and economic battle to combat a disease with no known cure and not much research being done on it, but also a political battle to mobilize knowledge and support around California.

In March 1999, wine industry members asked the Temecula City Council for a $25,000 research grant. The city responded with $125,000 and the Riverside County Board of Supervisors matched the amount. The American Vineyard Foundation received a $250,000 research grant for the University of California (UC) at Riverside to explore options to control PD.

Three people emerged as part of the local leadership: Joan Sparkman, vice president of Temecula Valley Bank and a local civic leader, Weaver, and Ben Drake, an agriculturist who manages vineyards in the Temecula area but also farms citrus and avocados. They contacted the UC Cooperative Extension, FDA, UC Riverside, the Farm Bureau, supervisors, state legislators, and local congressmen.

Drake and Weaver credit Sparkman with making a difference in the political fight. “We were just two farmers who wanted a solution,” recalls Weaver. “Sparkman had the connections and was not afraid to use them.” She enlisted the aid of Riverside County Assemblyman Rod Pacheco, who was able to mobilize support in the State Assembly and obtain $750,000 for three years for research.

Because he grew both grapes and citrus, Drake served as a bridge between two communities, which had different interests. Weaver, Sparkman, Drake, and others in the community were instrumental in creating an awareness around the state that Pierce’s disease and the GWSS posed a major threat to the grape and wine industry and the state’s economy.

In August 1999, culminating years of behind-the-scenes work, California Department of Food and Agriculture (CDFA) secretary Bill Lyons completed appointment of the CDFA GWSS/PD Task Force. The task force met for the first time at Callaway, shortly thereafter. Legislators attended, including Senator David Kelley, Assembly members Rod Pacheco and Bruce Thompson, and representatives from agriculture committees of both houses and the offices of Senator Wes Chesbro, Senator Raymond Haynes, and Congressman Ken Calvert. Drake and Weaver are members of the task force.

Out of this meeting and countless others, the wine industry became aware of the problem and the legislature focused funds on research. It took Temecula growers a few years to learn that the huge infestation of bugs represented a new vector for an incurable disease, but through their efforts, the rest of the state was made well aware of the problem. A total of $10 million has since been funneled into research for a cure.

More money has recently been made available to pay grapegrowers for vine losses. In March 2002, the CDFA announced implementation of a Grapevine Loss Assistance Program. This program gives money to up to 370 grapegrowers in the four worst hit counties (Kern, Riverside, San Diego, and Ventura) to compensate for documented losses due to GWSS-spread Pierce’s disease. Up to $7.14 million were made available for this program. Provisions of the program were contained in Assembly Bill 1242 authored by Assembly Member Patricia Wiggins (D-Santa Rosa).

Growers had to document up to 30% infection, the vine loss had to be due to Pierce’s disease spread by GWSS after August 1999, and vines were removed by May 1, 2002. Vineyard replacement costs per acre were determined by each county. Vines over 10 years old when removed got a 3% deduction for each year beyond 10 years.

Getting infected wood out early
Early on in the fight, Professor Alexander Purcell (Division of Insect Biology, Department of Environmental Science at University of California, Berkeley) told Temecula growers that the best way to control PD was to remove infected vines. Leaving vines standing allows disease-free insects to become infected and thus spread the disease to other vines.

Temecula’s willingness to pull out diseased vines early may prove to be its salvation. Weaver pulled out about 270 (40%) of Callaway’s 670 acres in the Temecula area. Peter Poole at Mt. Palomar removed 30 of his 90 acres of vines.

Between 1999 and 2000, wine grape acreage in Riverside County decreased 17%. For white wine, the acreage decreased 22%.

Hitting trouble spots early and hard
Temecula growers were also willing to hit the vines and adjacent citrus with insecticides. They felt they were in a war in which halfway measures would not work.

Early research suggested that a native parasitic wasp could make great strides against the GWSS by parasitizing the eggs, but the wasps will only be part of an integrated pest management solution for several reasons. At least four species of parasitic wasps, Gonatocerus ashmeadi, G. triguttatus, Gonatocerus fasciatus, and G. morelli have been studied in relation to knocking down GWSS.

Mark Hoddle, UC Riverside entomologist, reports that interest in morelli has waned, while interest in triguttatus has increased. At least two generations of sharpshooters are produced each year, a spring and a summer generation. Most of the wasps are effective on the second generation, but success depends on their effectiveness on the spring generation.

Several of the wasps were 98% to 100% effective on the summer generation, but somewhat less so on the spring generation. The triguttatus seems to be more effective on the spring generation and therefore holds more interest. Any IPM program including wasps accepts that some GWSS will remain, and a key is timing of chemical spraying to effectively manage them and keep insecticide use to a minimum.

A consensus decision was reached that the wasps alone were not the way to knock down the sharpshooters coming out of citrus groves. Winegrowers and citrus growers worked in concert with UC Riverside and the CDFA to develop a pilot program.

In 2000, part of a CDFA pilot program spent $360,000 to monitor and treat 1,600 acres of citrus in Temecula Valley. About 234 acres adjacent to vineyards were sprayed by helicopter with Lorsban, the trade name for a chemical called chlorpyrifos, a broad-spectrum organophosphate insecticide.

In 2001, $299,000 was spent for trapping and to apply Admire to citrus through irrigation. Helicopter spraying was done between 7:30 and 11am on Saturdays when there was less than a five mph wind.

Admire™ insecticide was applied on citrus through the irrigation system. It is designed to kill young sharpshooters in the spring. In the vineyards, Provado, another insecticide, was used.

Prior to this massive effort, Temecula prided itself on a low input, sustainable approach to agriculture. Pesticide applications in 2000 have so reduced the GWSS population in Temecula that scientists now have to go to the Arvin/Bakersfield area to find sufficient bug populations to study.

Conclusion
Drake, Weaver, and other Temecula growers have also helped mobilize a state into action. Because of the concerted calls-to-action of many in the Temecula area and the resulting response from the CDFA, University of California, the California Legislature, USDA, and the rest of the state, enormous brain power and research resources have been brought to bear on the Pierce’s disease problem.

Everything from antibiotics to pesticides, from native parasitic wasps to sprays and oils are being tested. Because of the willingness to get rid of unhealthy vines, infection spread has been slowed. Because of a concerted spraying effort in 2000, the infestation of sharpshooters is significantly reduced. But it seems clear that, at least, Temecula Valley has a fighting chance.

Drake has two vineyard trials to explore grapegrowing with PD. In March 2002, a new three-acre trial block of Syrah was planted with 110R rootstock. There was one irrigation at end of April with Admire™ added. Several vine rows received 16-oz. per acre plus a second application to deliver annual maximum of 32-oz. per year. Several vine rows received a total of 20-oz. of Admire™ per acre. Drake’s goal is to have 4ppm residual of Admire™ in the xylem tissue that would kill sharpshooters if attacked.

Drake’s second trial is one acre of five-year-old Cabernet Sauvignon on 110-R rootstock. There is a comparison/analysis of adding Admire™ or Platinum to irrigation water and an evaluation of application by drip from standard hose or with spaghetti extensions to deliver irrigation under mulch on the ground to insure delivery of material to the root zone in the soil.

Weaver has a seven-acre trial for badly damaged sections of the home vineyard adjacent to the Callaway parking lot. Callaway has planted to test five different treatments, with one control, in three irrigation blocks. Two rootstocks, 101-14 and 5BB, will be used with Clone 7 Cabernet Sauvignon spaced 8X8.

The five treatments include one trial with a balanced fertility program to see if PD can be successfully combated with fertilizers only.
One aspect of these trials that excites Weaver is that they involve a commercial vineyard, not a laboratory, greenhouse, or field station. Trials done in more controlled settings may get promising results, but those same results do not obtain outside a controlled environment, in the complicated and hectic reality of a commercial vineyard.