Phyto-pathogenic bacteria are a constant threat to plant health, causing diseases which lead to significant loss in grapevine production. A new way of fighting against pathogenic agents is using biological methods, as preimmunization with a virulent or weakly virulent sources and microbial antagonism, or with products of their metabolic activity. Currently, few products are used in the biological fight against phyto-pathogens, as most biological products and/or methods are currently under research.The paper presents aspects of the research carried on in order to establish the virulence of bacteria in the Bacillus spp. genus, in field-growing conditions, for further utilization of a viable method of fighting against the Agrobacterium tumefaciens pathogenic agent in grapevine.