Fire blight control strategies in organic fruit growing

Abstract

In organic fruit growing effective control strategies are needed to prevent blossom infections by the fire blight pathogen Erwinia amylovora. In a research project, funded by the “Bundesprogramm Ökologischer Landbau”, 44 different preparations have been tested. In nine field trials conducted since 2004 according to EPPO guideline PP1/166(3) BlossomProtect and MycoSin had the highest efficiencies. BlossomProtect contains blastospores of Aureobasidium pullulans, which, as a fungus, is sensitive to fungicides including sulphur that are used for apple scab control. In some cases, it enhanced fruit russet. Spray strategies, in which BlossomProtect was alternated with sulphur fungicides did not hamper the efficiency of BlossomProtect against fire blight. However, up to 8 applications had to be done during bloom to achieve fire blight and scab control. As MycoSin is known to enhance the efficacy of sulphur against apple scab and there is a proven effect against fire blight, a strategy to alternate BlossomProtect applications with sprays of a mixture of Netzschwefel Stulln and MycoSin was tested in field trials 2008 and 2009. With this strategy the total number of applications during bloom could be reduced to four, with only a slight decline in fire blight control. In addition, the number of applications of BlossomProtect was reduced from four to two in this strategy and thus, the risk of fruit russet declined.