Control of Botrytis cinerea in strawberries by biological control agents applied as single or combined treatments

There is little knowledge about the effects of simultaneously applied biological control agents (BCAs) on the incidence of grey mould (Botrytis cinerea) in strawberries under field conditions. Our objective was, therefore, to investigate the use of three BCAs (Bacillus amyloliquefaciens FZB42, Aureobasidium pullulans DSM 14940 and DSM 14941 and Beauveria bassiana ATCC 74040) with respect to their efficacy against B. cinerea in field grown strawberries following single compared to combined application. In two subsequent years (2011 and 2012), improved control of B. cinerea resulted from combined BCA treatments, whereas the single BCAs were not efficient. Efficient combinations of BCA treatments were not the same in 2011 and 2012, however. The development of B. cinerea was reduced by single treatments of B. amyloliquefaciens and A. pullulans as well as by most combined BCA treatments during storage for one of two fruit samples in 2011. In 2012, however, no effects on B. cinerea during storage resulted from BCA treatments. The results of the present study suggest that the use of combined BCA treatments only cannot overcome inconsistent efficacies of BCAs against strawberry grey mould under field conditions. Further investigations on the interactions between the BCAs in combined BCA treatments as well as between the BCAs and the pathogen in dependence on multiple factors prevailing in the phyllosphere, however, need to be included to tailor combined BCA treatments with constant efficacies in different years.