Introduction

100 percent of the vines in this two-year-old Temucula vineyard are infected with Pierce's Disease

In the summer of 1999, winegrape growers in Riverside County experienced the sudden die-back of grapevines in a number of vineyards in the Temecula Viticultural Area.  By mid-August more than 300 acres of vines near Temecula were dead or dying and University of California scientists confirmed that Pierce's disease (PD) was the cause.  In early October UC President Richard C. Atkinson established the Pierce's Disease Research and Emergency Response Task Force to mobilize the scientific, technical and information-outreach expertise of the University to find solutions to this serious problem.

Pierce's disease is caused by a bacterium (Xylella fastidiosa) that clogs a plant's xylem and effectively shuts down its ability to take in water and nutrients.  The disease  itself is not new to California.  It was first recorded  in the 1880s when it destroyed more than 40,000 acres of young grapevines in the Los Angeles basin. "Hot spots" of Pierce's disease also have persisted in the Napa Valley since the 1880s.  There have been periodic epidemics over the last century where the disease has reached a higher incidence and become more widespread in the grape-growing regions of the state.

In the early 1990s winegrape growers in Napa and Sonoma counties again began reporting symptoms of Pierce's disease in their vineyards. The spread of PD into North Coast vineyards, while widespread, is mostly confined to vines planted along riparian (streambank) areas and near irrigated landscapes. The principal insect vector coming from these habitats is the blue-green sharpshooter (BGSS).  Since 1994 more than 1,000 acres of PD-infected vines have been pulled and replanted, with an estimated cost to growers in excess of $30 million. 

The recent outbreak of Pierce's disease in the Temecula Valley, which has cost growers millions of dollars, is all the more troubling because the bacterium is transmitted by the glassy-winged sharpshooter, an exotic pest accidentally introduced into Southern California around 1989. Unlike the blue-green sharpshooter which is not a strong flyer, GWSS is an aggressive flyer - a trait which increases the spread of Pierce's disease over larger portions of vineyards.

There is growing concern that GWSS, now detected as far north as Santa Barbara County on the coast and Kern County inland, may spread Pierce's disease throughout the state's grape-growing regions.  If this was to occur, production would be threatened on more than 700,000 acres of wine, raisin and table grapes valued at $2.8 billion a year. There is no practical cure for Pierce's disease, with most vines dying within two years of being infected.  Besides grapes, many other economically important commodities grown in California may be at risk from other strains of X. fastidiosa.

UC researchers, supported by the Viticulture Consortium Program, California Competitive Grant Program for Research in Viticulture and Enology, American Vineyard Foundation and North Coast Pierce's Disease Task Force, have been studying ways to deflate the PD epidemic since the mid-1990s. Until recently the primary focus of these research efforts has been on the North Coast epidemic, with selective removal of riparian vegetation, introduction of new pest management strategies, winter pruning, and the application of micronutrients and antibiotics to vines showing the most promise for controlling BGSS and the X. fastidiosa bacterium.

As the magnitude of the problem in Riverside County became apparent, many organizations moved to provide funds to study the glassy-winged sharpshooter and its role in spreading PD.  The UC-managed Viticulture Consortium approved funding in spring 1999 for research into GWSS population dynamics and the incidence of PD in Temecula vineyards.  Local governments and industry raised another $250,000 over the summer.  In October Governor Davis signed AB 1232 (Chapter 627 of the Statutes of 1999) which provides $2.25 million in state funds over the next three years to support Pierce's disease research. The urgency bill requires industry to contribute another $750,000 for a total of $3 million in new funds.

The California Department of Food and Agriculture (CDFA) and the University each appointed a task force to address the Pierce's disease crisis.  The CDFA Glassy-Winged Sharpshooter/Pierce's Disease Task Force was established by Secretary for Food and Agriculture Bill Lyons, Jr., in September 1999.  Members were from CDFA, the winegrape industry, universities (UC and CSU), county agricultural commissioners, and the U.S. Department of Agriculture (USDA).

The primary focus of the CDFA task force was on the glassy-winged sharpshooter and slowing the spread of Pierce's disease in Southern California.  The task force members identified a series of research objectives and ranked them as high, medium or low priority.  Their report was delivered to Secretary Lyons in November.

In announcing his appointment of the UC Pierce's Disease Research and Emergency Response Task Force in early October, Atkinson cited the economic losses to California's wine and grape industries from PD and the University's commitment to work with growers to control this threat to the state's agricultural economy.

He asked the Task Force members to:

• identify promising areas for research and to formulate a set of science-based research priorities for tackling the disease and its insect vectors;
  
  
• report on activities by UC scientists and farm advisors to extend PD-related technical assistance to vineyard operators; and 
  
  
• identify other educational information needs of user communities and strategies for speeding the flow of science-based information into the field.

The 12-member task force, chaired by Vice President - Agriculture and Natural Resources W.R. "Reg" Gomes, included scientists from the Berkeley, Davis and Riverside campuses and county advisors from UC Cooperative Extension. Appendix I includes the October 6, 1999, press release announcing the Task Force and a roster of members.

The first meeting of the Task Force was in Oakland on October 15; the second at UC Berkeley on November 23.  A subcommittee of the Task Force met at UC Riverside on October 29.  During these meetings, information on the magnitude of the Pierce's disease epidemic on the North Coast and in Southern California was reviewed.  The Task Force members developed a detailed list of research needs and priorities, made decisions on the publication and distribution of a GWSS informational brochure, and developed a set of recommendations intended to increase the University's research and educational outreach activities in response to the PD crisis in California.

The report that follows summarizes the findings and recommendations of the Task Force.  It also provides background on the disease and the status of research and educational outreach efforts now under way in the University.  The report is organized under five sections.

• Section I.    Pierce's Disease and Its Vector
  
  
• Section II.   Current Research on Pierce's Disease and Vectors
  
  
• Section III.  Educational and Technical Assistance from UC
  
  
• Section IV.  Research Needs
  
  
• Section V.   Task Force Recommendations
  
  
• Section I.      Pierce's Disease and Its Vectors