Prior research has shown pathogen prevalence on-farms is not uniformly distributed, instead pathogen prevalence is highly dependent on environmental factors and management practices. A study was performed to determine environmental factors (e.g., landscape features, meteorological events) and management practices (e.g., date of last irrigation, pesticide application) that may impact the prevalence of Salmonella spp. and Listeria spp. at the sub-field level (0.2 ha grids) on an Eastern Shore of Virginia farm. Virginia Tech's Eastern Shore Agricultural Research and Extension Center (ESAREC) farm was used due to the liability of testing for pathogens in commercial produce fields; however, production practices used at the ESAREC farm are similar, if not the same, to production practices used on commercial farms. Fifteen drag swab, one water, and up to five fecal samples were collected every two weeks per sampling occurrence from August to December 2016 (thus up to 21 samples may be collected during one sampling occurrence. Samples were collected from randomized field plots that were picked during each sampling occurrence. Salmonella spp. and Listeria spp. were isolated and confirmed using modified versions of the Food and Drug Administration's Bacteriological Analytical Manual. Environmental factors were retrieved by remotely-sensed data for the sample location or date. Management practices were recorded by an observational survey for each sample occurrence.

Two hundred and seventy-four samples (210 drag swab, 50 fecal, and 14 water samples) were collected during the late summer, fall, and winter. Listeria spp. and Salmonella spp. was detected in 8.3% (23/274) and 1.8% (5/274) of samples, respectively. Neither pathogen was detected in any of the fourteen water samples tested. Findings from this study will support the development of mitigation strategies to reduce pathogen contamination on-farm, with emphasis at the sub-field level. For instance, mitigation strategies include growers electing to not harvest near edges of fields or directly after precipitation events to minimize contamination events. Additionally, management practices were found to be associated with pathogen prevalence; therefore, management practices should be carefully tailored for each unique farm landscape.