EPIDEMIOLOGY OF XYLELLA FASTIDIOSA DISEASES IN CALIFORNIA

• Author(s): Bartels, David; Civerolo, K.; Luvisi, J.; Puterka, Gary; Wittenborn, G.;
• Abstract: Incidence of Pierces disease (PD), caused by Xylella fastidiosa, continues to increase in many grape varieties in California due to the establishment and spread of the vector, the glassy winged sharpshooter, Homalodisca coagulata. Eleven vineyards were surveyed during the 2001 and 2002 production seasons. Each vineyard was assessed visually for PD symptoms and geo-referenced using GPS technology. Commercially available materials [e.g., Particle film barrier (Surround WP) containing 95% kaolin and systemic acquired resistance inducer (Messenger) containing 3% harpin] were also evaluated for their effects on reducing X. fastidiosa transmission, and preventing X. fastidiosa infections and PD development. The spatial patterns of Pierces disease epidemics in grower-managed vineyards naturally affected by PD were analyzed by ordinary runs, indices of dispersion, and two-dimensional distance class analyses. Disease incidence ranged from 1% to 80%. The spatial disease gradient analyses consistently described the non-randomness of the patterns of diseased vines, and an increase in the degree of clustering of diseased vines as disease incidence increased. Three grapevine varieties (Flames Seedless, Chenin Blanc, and Thompson Seedless) in four blocks were treated on March 13, March 30, and April14, 2001, with Surround WP. During the 2-year study, PD development was lower (6%) in Surround treated plots than in conventional insecticide treated plots (14%). No Surround by grapevine variety interaction was observed in either year. PD incidence among grapevines in a commercial field in Tulare County was 13%, 7%, and 6% with 2.25, 4.50 and 6.50 oz Messenger, respectively. PD incidence in untreated control vines was 18%. Based on these results, effective PD management is likely to be based on practices that reduce initial inoculum and use of resistant varieties. Also, X. fastidiosa-infected vine removal and monitoring of surrounding vines for new X. fastidiosa- infections should be practiced. A greenhouse study to determine the effects of Surround, Admire and Messenger on X. fastidiosa transmission and PD development is currently in progress.
• Publication Date: Dec 2002
• Journal: 2002 Pierce's Disease Research Symposium