In the present investigation the in vitro activity of nanoemulsion (AUSN1) was evaluated against the plant pathogen Pectobacterium carotovorum sub sp. carotovorum causing the soft rot disease in numerous horticultural crops. With AUSN1 nanoemulsion treatment, minimum inhibitory concentration (MIC) of 0.09 mg ml−1, minimum bacteriostatic concentration (MBC) of 1.30 mg ml−1 and zone of inhibition of 2.90 cm was observed against P. carotovorum. This formulation was able to reduce the bacterial population by 32.2–51.6%, under biofilm formation condition and a complete elimination of population under normal cultivation conditions. When subjected AUSN1 treatment, reduction in biofilm formation, swarming and swimming motility was observed in P. carotovorum strain and also inhibited the N-acyl homoserine lactones (AHL) activity by 13.27–62.3% and AHL production by 32.4–76.13%. Reduction in exo polysaccharide (EPS) synthesis and hydrolytic enzymes production in P. carotovorum strain was observed due to AUSN1 treatment. Reduced hydrophobicity (36.9–56.4%) and adhesion to polystyrene (22.9–47.5%) and potato tuber surfaces (19.5–46.8%) was observed with AUSN1 treatment. All these collective evidences clearly show that, under laboratory conditions, AUSN1 treatment was able to inhibit the soft root incidence in potato tubers.