|HAVILAND, DAVID - University Of California - Cooperative Extension Service|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2020
Publication Date: 4/28/2020
Citation: Sisterson, M.S., Burbank, L.P., Krugner, R., Haviland, D., Stenger, D.C. 2020. Xylella fastidiosa and glassy-winged sharpshooter population dynamics in the southern San Joaquin Valley of California. Plant Disease. https://doi.org/10.1094/PDIS-01-20-0066-RE.
Interpretive Summary: Diseases caused by Xylella fastidiosa are a threat to production of perennial tree and vine crops worldwide, including almond leaf scorch, citrus variegated chlorosis, olive quick decline, and Pierce’s disease of grapevine. Epidemics of Pierce’s disease in the southern San Joaquin Valley of California are associated with high abundance of the invasive glassy-winged sharpshooter that transmits X. fastidiosa from plant to plant. A field study was conducted to determine the time of year that vine-to-vine transmission of X. fastidiosa is most likely to occur. Grapevines known to be infected with X. fastidiosa were more likely to test positive in July and August than in spring, suggesting that acquisition from chronically infected grapevines is unlikely to occur until July. Similarly, more glassy-winged sharpshooters tested positive for X. fastidiosa in July and August than in spring. Accordingly, risk of vine-to-vine spread of X. fastidiosa is greatest in July and August. Results will improve timing of insecticide applications to reduce glassy-winged sharpshooter populations, thereby reducing spread of X. fastidiosa.
Technical Abstract: Xylella fastidiosa is a vector-transmitted bacterial plant pathogen that affects a wide array of perennial crops, including grapevines (Pierce’s disease). In the southern San Joaquin Valley of California, epidemics of Pierce’s disease of grapevine were associated with the glassy-winged sharpshooter. During the growing season, rates of X. fastidiosa spread in vineyards are affected by changes in pathogen distribution within chronically infected grapevines and by vector population dynamics. Grapevines chronically infected with X. fastidiosa rarely tested positive for the pathogen prior to July, suggesting vector acquisition of X. fastidiosa from grapevines is likely to increase as the season progresses. This hypothesis was supported by an increase in number of X. fastidiosa positive glassy-winged sharpshooters collected from vineyards during July through September. Analysis of insecticide records indicated that vineyards in the study area were typically treated with a systemic neonicotinoid in spring of each year. As a result, abundance of glassy-winged sharpshooters was typically low in late spring and early summer, with abundance of glassy-winged sharpshooter adults increasing in late June and early July of each year. Collectively, the results suggest that late summer is a crucial time for X. fastidiosa secondary spread in vineyards in the southern San Joaquin Valley as glassy-winged sharpshooter abundance, number of glassy-winged sharpshooters testing positive for X. fastidiosa, and grapevines with detectable pathogen populations were all greatest during this period.