A well-known method used in the identification of potent bacterial antagonists is to test in vitro activity by plating potential antagonist with the pathogen and evaluate the inhibition of pathogen growth (i.e. zone clearing assays). However, we hypothesized that relying on this method might miss other potential antagonists that do not rely on antibiotics production. In this study, we examined the ability of 52 different Pseudomonas strains to limit the formation of hairy root disease (HRD) caused by Agrobacterium rhizogenes. HRD is a problem on hydroponic grown tomatoes and cucumbers in Europe and North America. Our Pseudomonas collection was screened in both in vitro (zone clearing assays) and in planta (reduced disease formation) assays. Our in vitro studies identified fourteen Pseudomonas strains that exhibited zone clearing activity. These strains were then tested in planta from which we identified two that were effective in reducing disease incidence in tomato under soil and hydroponic conditions. We also screened the remaining collection in planta on tomato aiming to identify strains that may have been missed in the in vitro study. From this study we identified five additional strains that were effective in reducing disease incidence on soil (hydroponic tests are underway). In conclusion, in vitro, screening is helpful to identify potential strains, however, many other strains with other potential modes of actions could be lost during the process.