Xanthomonas hortorum pv. carotae (Xhc) causes bacterial blight of carrots and carrot seed crops. Xhc can colonize plants epiphytically without causing symptoms, but still resulting in infested seed. A biocontrol agent that inhibits the growth of Xhc on plants in the field could reduce pathogen populations and subsequent seed lot infestation. Nine bacterial isolates originating from carrot seeds or plants and exhibiting biocontrol potential in vitro were identified using 16S DNA sequences and screened for the ability to inhibit Xhc growth on carrot plants in the greenhouse. Amplification of the partial 16S rDNA gene using primer pair 1627R/161492R resulted in products 627-1404 bp in size. BLASTn results from the GenBank Database identified four Pantoea spp., three Pseudomonas spp., one Enterobacter sp., and one Flavobacterium sp. A significant (P<0.0001) effect of bacterial isolate on Xhc growth was observed on carrot leaves using viability quantitative PCR. Negative binomial regression parameter estimates for Pseudomonas isolates Pss 422 and 17-049 were negative and significantly less than zero (P?0.0001), indicating that these isolates reduced Xhc colonization on carrot foliage. In contrast, the parameter estimate for isolate 16-297 was positive and significant (P=0.045), suggesting that the isolate increased Xhc growth on carrot leaves. Further testing is needed to determine the potential for biocontrol of bacterial blight, especially under field conditions.