Abstract
In the present study the plant strengthener compound RioZell-2000B/Aksebio 2 was tested on its effect against fire blight (Erwinia amylovora) as a possible alternative to streptomycin. First in in vitro studies (in agar diffusion test) no inhibiton effect against the pathogen was found. Under greenhouse conditions with the highly susceptible M26 rootstock BioZell-2000B treatment resulted in a marked decrease of the disease rate of 58% and was correlated with a reduction of the bacterial growth up to 49.5%. Further studies in the field under natural infection conditions during full bloom with apple cultivar 'Roskoop' resulted in a control effect of Biozell-2000B of 52%. In another trial on the highly susceptible Cotoneaster salicifolius, under experimental infection conditions, an efficacy of 84% could be confirmed during blossom time.