March 31, 2025 — According to a study released today, the California Department of Food and Agriculture’s Pierce’s disease (PD) and glassy-winged sharpshooter (GWSS) prevention, control and research efforts save California winegrape growers $56 million annually by reducing losses from the fatal grapevine disease. Without the program’s efforts, growers’ losses would more than double from $48 million to $104 million.
The study conducted by the UC Davis Robert Mondavi Institute Center for Wine Economics found that if GWSS spread unchecked, outbreaks of PD could cost winegrape growers an additional $56 million a year in lost production and vine replacement. Read “The Costs of Pierce’s Disease in the California Grape and Wine Industry.”
“This study highlights the serious threat Pierce’s disease and the glassy-winged sharpshooter pose to our industry and reinforces the importance of grower-funded research,” said Randy Heinzen, a Paso Robles winegrape grower and chair of the Pierce’s Disease and Glassy-Winged Sharpshooter Board. “The public-private partnership led by the Pierce’s Disease Control Program is vital, allowing grower assessment funds to drive research that improves pest and disease management and to develop practical, sustainable solutions for the long-term viability of our industry.”
The unique funding partnership the winegrape industry forged between growers, the state and federal government and industry fuels the essential research and control operations that have significantly blunted the most severe impacts of PD and GWSS. Even with these efforts, PD still costs an estimated $110 million annually in California, including $45 million for control, prevention and research, $48 million in lost winegrape production and vine replacement and $17 million in lost table and raisin grape production and vine replacement. Without these critical programs, the industry’s losses in production and vine replacement would be even higher, putting greater financial strain on growers and threatening the long-term stability of California’s vineyards.
“The economic data is clear as day — an ounce of prevention is worth a pound of cure,” said Joseph Damiano, statewide coordinator for the Pierce’s Disease Control Program. “For a quarter of a century, growers, government and industry partners have invested in research and treatments to keep PD and GWSS at bay. This study shows the return on that investment, and it’s pretty impressive.”
With industry and government support keeping PD and GWSS in check, grower-funded research continues to drive advancements in pest and disease management while supporting field trials for promising solutions. According to the study’s authors, the economic burden of PD and GWSS could decrease as this research yields practical, vineyard-ready innovations.
“Agricultural research and development takes a long time to bear fruit,” said Dr. Julian M. Alston, lead author of the study. “But once it does, its benefits can continue to pay dividends for decades. While it is too soon for some Board-funded research developments to be brought to vineyards, great progress has been made in PD/GWSS management and five PD-resistant winegrape varieties have already been released.”
About the PD/GWSS Board
The PD/GWSS Board ensures winegrape grower assessment funds are spent wisely and productively to find solutions to PD, GWSS and other designated winegrape pests and diseases. The annual assessment rate has held steady at $1.25 per $1,000 of crop value for the past three years. Since 2001, the PD/GWSS Board has invested over $57.7 million in 298 research projects, with three-quarters of the funds exclusively spent on PD/GWSS. The remaining investments have further reduced losses from other pests and diseases, including red blotch, leafroll, and mealybugs. For additional information, visit cdfa.ca.gov/pdcp/PD_GWSS_Board.html.
