Extensive efficacy tests of non-antibiotic fire blight control agents

Application of control agents to prevent new infections is an integral part of disease management for fire blight on pome trees caused by Erwinia amylovora (Burrill) Winslow et al.. Due to resistance development and human health concerns when using antibiotics, non-antibiotic control agents with high efficacy are urgently needed. In this study extensive efficacy tests with some classical antibiotic and relatively new non-antibiotic control agents for the prevention of bloom and shoot blight as well as phytotoxicity tests based on fruit russeting were carried out using young apple trees. Furthermore an experimental design for testing control agents preventing fire blight following hail injury was developed. The high efficacy of streptomycin (> 90%) and streptomycin containing spray strategies (> 80%) was confirmed. Non-antibiotic agents with high efficacy are LMA (85%), a potassium aluminum sulfate, and Juglon (80%). LMA is already in use in practice in Austria and Germany with a temporal and restricted permission and the administrative process to gain the legal status of a pesticide is ongoing whilst already admitted in Switzerland. Juglon, an organic compound from walnut, did show a high efficacy, but no consistent results (80.0 and 69.5%). Myco-Sin showed good results to prevent infection after artificial hail simulation. Antinfek showed high efficacy (90%) in preventing bloom blight, but could be tested only once so further research is needed to confirm this result. The design of the presented study enabled an extensive evaluation of the potential control agents and the aggregation and comparison of results and can be advised for other evaluations.