Assessing effects of seasonality on the epidemiology of Pierce’s disease in the southern San Joaquin Valley

Authors: Sisterson, Mark; Burbank, Lindsey; Krugner, Rodrigo; Stenger, Drake

Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 10/27/2017
Publication Date: 12/12/2017
Citation: Sisterson, M.S., Burbank, L.P., Krugner, R., Stenger, D.C. 2017. Assessing effects of seasonality on the epidemiology of Pierce’s disease in the southern San Joaquin Valley. CDFA Pierce's Disease Control Program Research Symposium. p. 149.

Interpretive Summary:

Technical Abstract: Introduction of the glassy-winged sharpshooter to California resulted in epidemics of Pierce’s disease in the Temecula Valley and the southern San Joaquin Valley in the late 1990’s and early 2000’s, respectively. In response, an area-wide suppression program was initiated that successfully suppressed glassy-winged sharpshooter populations from 2002-2011. Since 2011, population levels of glassy-winged sharpshooter have been high in some locations in the Southern San Joaquin Valley, resulting in increased levels of Pierce’s Disease. A field study was initiated in the spring of 2016 to identify the time of year that glassy-winged sharpshooters are most likely to acquire and transmit Xylella fastidiosa (Xf). To accomplish this, 4 citrus orchards and 4 vineyards were sampled every three weeks beginning in April of 2016. On each visit, abundance of glassy-winged sharpshooter on ten citrus trees or ten grapevines was assessed. In addition, glassy-winged sharpshooters were collected and tested for presence of Xf by quantitative polymerase chain reaction (qPCR). Finally, plant samples were collected at vineyard sites from chronically infected grapevine to determine seasonal changes in Xf population densities in plants. In 2016, abundance of glassy-winged sharpshooter was high at vineyard and citrus sites. Specifically, 536 sharpshooters were collected from citrus locations and 146 sharpshooters were collected from vineyards during 2016, with 74 (14%) and 28 (19%) testing positive for Xf. The number of Xf-positive sharpshooters in 2016 was low from April to late July and markedly increased in late July through early September. The timing of the increase in Xf-positive sharpshooters occurred simultaneously with an increase in qPCR detection in grapevines chronically infected with Xf. At citrus sites, the highest percentage of Xf-positive sharpshooters was observed in late fall and early winter. In 2017, abundance of glassy-winged sharpshooters had declined at collection locations, presumably due to area-wide insecticide treatments. During 2017, 314 sharpshooters were collected from citrus sites and no sharpshooters were observed at vineyard sites. At citrus sites, 36 (11%) of sharpshooters were Xf-positive with the highest percentage of Xf-positive sharpshooters observed in late winter and early spring. Sampling is ongoing and will end in fall of 2018.