AREA-WIDE MANAGEMENT OF THE GLASSY-WINGED SHARPSHOOTER IN THE TEMECULA AND COACHELLA VALLEYS

• Author(s): Gispert, Carmen; Hix, Raymond; Toscano, Nick;
• Abstract: Riverside County has two general areas where citrus interfaces with grape: 1) the Coachella Valley with about 14,000 acres of table grapes and 12,000 acres of citrus; and 2) the Temecula valley with 1800 acres of wine grapes in proximity to 1600 acres of citrus. Xylella fastidiosa was recently recovered from the Coachella Valley (Perring and Gispert, unpublished), and the glassy-winged sharpshooter (GWSS) is very abundant. In Riverside County, table and wine grapes are the most vulnerable crops to GWSS as a vector of the bacterium Xylella fastidiosa, the causal agent of Pierces disease (PD). Perhaps more than any other source, citrus is viewed as an important year round reproductive host of GWSS, but also one that concentrates GWSS populations over the winter months during the time that grapes and many ornamental hosts are dormant. Temecula. The Temecula viticultural area was the first in California to be seriously impacted by the glassy-winged sharpshooter (GWSS) Homalodisca coagulata and the spread of X. fastidiosa, the causative agent for PD. While PD problems were first identified in 1996, it was realized by 1999 that the situation was dire. As a result, this ongoing cooperative demonstration project was initiated in 2000 to examine the impact of area-wide management strategies on GWSS populations and PD incidences in the Temecula Valley. The Temecula advisory committee consists of representatives from wine grape growers, citrus growers, University of California-Riverside, USDA, California Department of Food and Agriculture (CDFA) and the Riverside County Agricultural Commissioners Office. In the 2000 season, the opportunity to treat nearly the entire commercial citrus in the Temecula viticultural area was seized upon in an effort to destroy a substantial portion of the regional GWSS population. The emergency treatment of 1300 acres of citrus in Temecula, CA with Admire() (imidacloprid) during Apr and May 2000 represented a pivotal shift toward an area-wide management of GWSS. In March and April 2001, 269 acres of citrus were treated with Admire and an additional 319 acres were treated with foliar applications of Baythroid() on an as needed basis. Many grape growers treated their grapes with Admire and/or made foliar applications of Provado(), or Danitol() in 2002. Recommendations were made to remove sick vines in order to remove bacterial reservoirs. Though response was slow initially, growers are aggressively removing sick vines. Although wine and table grapes are the most vulnerable due to the risk of PD, other crops were scrutinized for contributions to GWSS population growth. Citrus was the most important year long reproductive host of GWSS in Temecula. Citrus also seemed to concentrate GWSS over the winter months when grapes and most ornamental hosts were dormant. Coachella. The table grape industry in the Coachella Valley is represented by 10,465 acres of producing vines, which generated grapes valued at $108.5 million in 2001. GWSS was identified in the Coachella Valley in the early 1990's, and increases in the numbers of this efficient PD vector over the past 15 months have been documented. In July 2002, the occurrence of X. fastidiosa (PD strain) in 13 vines from 2 adjacent vineyards in the southeastern part of the Valley was confirmed. With this discovery, and the increasing numbers of GWSS, there was a real need for an area-wide GWSS and PD management program, to prevent the devastating epidemic like which occurred in Temecula. Clearly, there are no apparent biological or climatological factors that will limit the spread of PD in grapes in the Coachella Valley. Obviously, GWSS had the potential to develop high densities in the Coachella Valley.
• Publication Date: Aug 2003
• Journal: 2003 Pierce's Disease Research Symposium