Studies were conducted to assess the extent to which natural disinfection reduces bacterial populations introduced to spinach production systems by irrigation. Four field trials were conducted using isolated spinach plots at a commercial growing operation. Nalidixic acid resistant Escherichia coli were introduced to spinach plots by a suspended irrigation system. E. coli NAR fate on plants and in soil was monitored over time. E. coli NAR applied at mid-day to intact spinach plants displayed reproducible rapid decreases in its culturability: 0.84 to 2.0 log10 reductions within 6 h of inoculation, undetectable at 24 to 72 h. The shielding of plants under a plastic canopy appeared to provide some protection against changes in E. coli: 24 h extension of detection period. Lab investigations indicated that E. coli NAR is sensitive to UV radiation, but to a notably lesser degree on spinach tissue than on glass: average 0.62 log10 reduction on cut spinach vs. 6.10 log10 decrease on glass. However such falls short of the 3.8 to 4.8 log10 reductions observed in the field. Further, single unit in tube assays failed to reveal any direct inhibitory effect of spinach leaf tissue itself or its complement of native bacteria on E. coli NAR. Recorded, but untested, lab observations suggest that desiccation may play a role in altering the culturability of E. coli NAR. A DNA detection/amplification procedure was utilized in attempts to confirm the presence of viable but not culturable E. coli in growth-negative plant extracts. However, the system was found to be lacking in the required specificity. Dreux, N., Albagnac, C., Carlin, F., Morris, C. and Nguyen-The, C. 2007a. Fate of Listeria spp. on parsley leaves grown in laboratory and field cultures.