Identification of factors mediating cold therapy of Xylella fastidiosa-infected grapevines. PRINCIPAL INVESTIGATOR AND COOPERATOR

LIST OF OBJECTIVES AND DESCRIPTION OF ACTIVITIES CONDUCTED TO ACCOMPLISH EACH OBJECTIVE Objective 1: Develop an experimental, growth chamber temperature regime that can consistently cure Pierce’s Disease affected grapevines without causing unacceptable plant mortality. The results described in previous reports show that our field plants and cold chamber plants showed lower disease ratings and higher curing rates in the colder temperature treatments. In 2005-2007 sites, vine mortality was minimal due to better cold acclimation of the grapevines prior to establishing the plots in the fall. The data collection for the field and cold chamber studies have been completed (Tables 1 and 2, respectively) and the analysis of the data to determine the critical temperature thresholds for cold curing has begun. We are continuing to work with Len Coop from the University of Oregon to generate a cold temperature model to determine if vineyards in cold boundary areas (i.e., foothills of the Sierra and northern-most California) are at risk for developing PD. The information obtained from these models could provide data that could be used by grape growers for risk assessment and management purposes. Field Experiment Results: The results for our field plots showed lower disease ratings and higher curing rates in the colder temperature treatments (Table 1). This is consistent with the results we obtained in previous field seasons. This information will be used to make a model that will help predict what areas are most likely to experience cold curing and not expected to have PD problems.