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POSTERS: Chemical control

Bacterial Spot of Peach: Chemical Sensitivity in Strains from Cankers, Leaves and Fruit
Brodie Cox - Clemson University. Guido Schnabel- Clemson University

Bacterial spot control on peaches in the Southeastern United States is caused by Xanthomonas arboricola pv. pruni (XAP) and has been a problem to manage for many years. In susceptible cultivars copper applications starting at delayed dormancy up to preharvest season is recommended. In addition, many growers also apply oxytetracycline for bacterial spot management. But even with best efforts, in years with frequent precipitation or high humidity after bloom the disease is very hard to control. It is unclear whether resistance development in XAP contributes to a lack of disease management success. The objective of this study was to collect XAP from cankers, leaves and fruit and investigate sensitivity to bactericides copper and oxytetracycline. Strains were collected from four farms located in the major peach producing areas of South Carolina which have experienced an increase in incidence of bacterial spot over the past years. XAP isolated from cankers, leaves, and fruit were assessed for sensitivity to copper and oxytetracycline using a spiral plater gradient. The bacterial strains from the various samples taken throughout the year illustrated high variability in bactericide sensitivity. The number of strains resistant to copper varied depending on the farm and spray history. The results demonstrate how diverse the sensitivity of XAP can be within an orchard block at different times of the growing season.