EPIDEMIOLOGY OF PIERCES DISEASE IN THE COACHELLA VALLEY

• Author(s): Gispert, Carmen; Perring, Thomas; Farrar, Charles;
• Abstract: The table grape industry in the Coachella Valley is represented by 14,400 acres of producing vines (California Department of Food and Agriculture 1999), which generated grapes valued at $131 million in 1998 (Jose Aguiar, Riverside County Farm Advisor, personal communication). In the past, Pierces disease (PD), a disease caused by the xylem-limited bacteria, Xylella fastidiosa Wells et al., has occurred in the Valley, but incidence has been limited to fields bordering weedy areas. X. fastidiosa is transmitted from infected to healthy plants by sharpshooters, a group of insects in the family Cicadellidae. In 1997, PD was documented in the wine grape-growing region of the Temecula Valley in southern California. Unlike the Coachella Valley and other areas in the state where PD is known to exist, the Temecula growers suffered devastating losses. A survey of 8 Temecula vineyards, conducted in September 2000 found plant decline or death due to PD ranging from 51%-87% (Perring et al. 2001). The most plausible explanation for the swiftness and severity of the PD epidemic in Temecula is the unique epidemiology created when the glassy-winged sharpshooter (GWSS), Homalodisca coagulata (Say) is introduced into an area with endemic PD sources (Purcell and Saunders 1999). When this occurred in Temecula, the epidemic mimicked the southeastern US, where GWSS-transmitted PD is the major factor limiting grape production. The glassy-winged sharpshooter was identified in the Coachella Valley in the early 1990s (Blua et al. 1999). There are no apparent biological or climatological factors that will limit the spread of PD in grapes in the Coachella Valley. Our work reported here was designed to document the current levels of PD in the Coachella Valley and to describe the seasonal cycle of the GWSS. This will allow us to identify characteristics of vineyards with high and low disease incidence for the purpose of designing strategies to minimize PD spread.
• Publication Date: Dec 2001
• Journal: 2001 Pierce's Disease Research Symposium