Fire blight control in organic fruit growing - systematic investigation of the mode of action of potential control agents

摘要

Effective control agents are needed to prevent blossom infections by the fire blight pathogen Erwiniaamylovora in organic fruit growing. In this study 18 preparations of potential control agents werecompared for their efficiency against E. amylovora. In shaken cultures twelve control agents inhibited thegrowth of E. amylovora completely. In this system different mechanisms of action were found. Sixcontrol agents shifted the pH of the cultures to values not suitable for bacterial growth (<5 or >8). Threeagents act by copper, a known bactericide. The control agent Elot-Vis has high ethanol content, whichwas responsible for the high efficiency in vitro. On detached apple blossoms only four control agents ledto a symptom reduction of more than 50%. Only two of them (Blossom-Protect fb, BPASc) exhibited ahigh efficiency in field trials. Our results suggest that the control agents, which led to a high efficiency inshaken cultures, are not sufficient for good performance in the field.