Xylella Fastidiosa Diseases
Xylella fastidiosa (various subspecies)
Overview
Xylella fastidiosa is a xylem-limited bacterium that causes several important plant diseases, including Pierce's disease of grape, almond leaf scorch, olive quick decline in some regions, and bacterial leaf scorch of landscape trees. Sharpshooters and spittlebugs transmit the bacterium while feeding on xylem sap. Strain and host combinations determine which plants are threatened in a given area. Once established in the xylem, the bacterium restricts water movement and produces chronic scorch and dieback.
Symptoms
Symptoms vary by host but commonly include marginal leaf scorch, yellowing, wilting of shoot tips, fruit shrivel, and progressive dieback. Grapes with Pierce's disease show leaf scorch with yellow or red margins, matchstick petioles after leaf drop, and drying clusters. Landscape trees may scorch sector by sector over years. Olive and other hosts can decline rapidly under some strain-host combinations. Vector insects may be present on succulent growth during the season.
Environmental Conditions
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Prevention
Plant resistant or tolerant cultivars and rootstocks where breeding programs have released them for your crop. Source clean nursery stock. Avoid moving host plants from infected regions. Monitor for sharpshooters and use exclusion screens in nurseries. Diversify plantings so a single Xylella disease cannot wipe out an entire landscape guild. Keep trees and vines vigorously but not excessively soft with nitrogen, which can attract vectors to tender flush.
Management
Remove chronically infected, severely declining plants that serve as pathogen reservoirs when recommended locally. Maintain irrigation to reduce drought stress that intensifies scorch. Manage sharpshooter habitat by reducing lush preferential weeds near vineyards and orchards when practical, while preserving beneficial insect resources. Prune out dead wood for safety. There is no simple home spray that clears Xylella from the xylem; focus on plant removal, vector pressure, and replacing with less susceptible species.