Twelve years ago a Pierce’s disease epidemic in Southern California wine grapes prompted a multi-pronged local, state and federal attack to contain the disease spread and find a cure or treatment. Today, the Pierce’s Disease/Glassy Winged Sharp Shooter Control Program is lauded as a highly successful model of results-driven cooperation between government agencies, citrus growers, nurseries and wine and table grape growers, university researchers and industry stakeholders.

Programs to control the Asian citrus psyllid/Huanglongbing and European grapevine moth follow its model. It has been expensive. $438.5 million has been spent so far.

Disease management protocols developed through the program have virtually eliminated vine-to-vine transmissions by the glassy winged sharpshooter (GWSS), the insect vector of Xylella fastidiosa, the bacterium that causes Pierce’s Disease — as long as growers stay alert and maintain best management practices. Area-wide programs fund monitoring, biological controls and insecticide treatments in citrus groves that harbor the GWSS. Grower assessments have supported fast-track research that identified plant hosts, led to development of PD-resistant vine varieties and discovery of compounds within the plants that appear effective at stopping or reducing the symptoms of the disease.

It could have been much different.

Paul Giboney graphically describes recognizing the widespread devastation that could be wrought by Pierce’s disease fully infecting his Kern County table grape vineyards. “We felt like we were standing in a pool of gasoline just waiting for the match to get lit,” he said.

Giboney and others from around the state had traveled to Riverside County to witness for themselves the ground zero of a disease that with amazing ferocity had gotten a stranglehold in Temecula Valley vineyards. Riverside County agriculture officials declared a local emergency in 1999 and 300 acres of Temecula wine grape vines were destroyed after they were found to be infested with the GWSS.

Within a year or so, Giboney and other Kern County growers were seeing vines dying in pockets in the Arvin and General Beale areas, and it “looked like the handwriting was on the wall.” These outbreaks were much more severe than California’s traditional patterns of PD.

Emergencies were declared, a task force was formed, and in 2000 $22.3 million in federal financial assistance was secured to reduce pest infestations and support research. The state Pierce’s Disease Control Program was officially established. Survey protocols and guidelines to use for finding infestations were created.  A website dedicated to Pierce’s disease and the GWSS set up by the California Department of Food and Agriculture received 500,000 hits in its first year online.

Northward march of GWSS

And still the seemingly inevitable northward march of the GWSS continued with infestations found as far north as Chico. Wine grape growers lobbied hard for an assessment that would help bolster research and fund a monitoring and control program. In 2001 a $3 per $1,000 value was enacted. For some, the assessment marked the official beginning of this highly cooperative program.

Nick Toscano is the University of California, Riverside, Extension entomologist who developed the original GWSS control proposal adopted by the CDFA. He continues to manage the tracking and reporting program in Temecula.

Tracking is key to the success of the management program, Toscano said. In Temecula, 450 yellow sticky traps monitor GWSS numbers and movements in citrus groves and vineyards. If even one adult GWSS is found in the weekly trap inspection a visual inspection is triggered. A weekly newsletter emailed to stakeholders alerts growers and managers to GWSS buildups at their sites and the need to initiate insecticide treatment to prevent GWSS populations from becoming established.

Research found that the Southern California epidemics were almost entirely the result of vine-to-vine transmission, a pattern rarely seen before the GWSS became established. Infections that occur in June and July have enough time to get established, survive the winter, causing PD during the next growing season. A protocol of applying one carefully timed application of a persistent systemic insecticide such as imidacloprid virtually eliminates the vine-to-vine spread.

Ben Drake is a Temecula-area wine grape grower and vineyard manager who began seeing problems from PD in the Temecula Valley as early as 1997. He and others in the area became key players in galvanizing the multi-pronged approach to the PD/GWSS threat. Drake was an inaugural member of the state task force and the PD/GWSS board, and continues to serve on both today.

“We’ve found that if we apply (imidacloprid) at the middle to the end of May, before the sharpshooter moves out of the citrus and goes into the vineyards, we get levels of the material into the plant high enough that when the sharpshooter flies over from the citrus groves to try it, they just fly back where they came from. Or, if they feed long enough, it will kill them.

“I’m not saying that we won’t find a vine that we will lose to Pierce’s disease, but we don’t have that epidemic level that we had in previous history.”

Lulled into complacency

The statewide strategy for slowing or stopping the spread of the GWSS and for finding solutions to PD has been so successful that growers sometimes get lulled into complacency.

This year, for example, Giboney said there’s been an uptick in PD again in the General Beale Road area. He attributes this to the “difficulty of treating the pest where we have an interface of different cropping patterns, windbreaks, and the importance of maintaining good weed management programs, rouging out infected vines and continuing to apply imidacloprid.”

It was discovered that a local grower hadn’t done any of those things, said Giboney, who also is the chairman of the Kern Tulare Consolidated Table Grape Pest and Disease Control District.

A similar experience quickly hit home with Nick Palumbo, a wine grape grower and winery owner in Temecula.

“A few years ago I learned my lesson,” he said. “I got cocky and said ‘We’re not seeing the bug anymore. There’s no more pressure.’ And I actually didn’t treat. But the following year I saw bugs, and so you really do have to monitor and keep up with treatments.”

Both instances point to the need to maintain ongoing and vigilant outreach and education programs, said Bob Wynn, director of the CDFA Pierce’s Disease Control Program.

“Our biggest fear is complacency, which is one of the downfalls of success,” said Wynn. “A lot of people think, ‘We’ve taken care of the problem because we haven’t heard about it.’  But that’s because we have ongoing management systems that take care of the problem. I mean 11 years ago you would never have guessed that (Temecula) would be expanding the plantings in that area.”

But just look at the Temecula Valley now to understand what’s changed: From 12 wineries in 1999, the Temecula Valley Winegrowers Association website today lists more than 50 growers and 34 wineries. All across the valley acreage is being cleared and new vines and varieties are being planted. A thriving agritourism industry has developed. Several wineries offer full-service accommodations along with golf packages and spa and wedding facilities. Existing wineries are expanding and new ones are under construction or in planning phases.

“Everyone can be proud of the cooperation that occurred between all these different stakeholders,” said Giboney. “This program has resulted in a significantly reduced level of PD and populations of GWSS.”