Purpose: This study evaluated irrigation (overhead and drip) and water treatment (with or without chlorine dioxide) on pathogen presence and indicator organisms within an organic farming system.
Methods: Sampling of open surface water used for irrigation (free flowing and with sediment) was performed. Water samples were collected at the point of application in the treatment plots during four irrigation events, 4 plots per treatment (overhead untreated, drip untreated, overhead with chlorine dioxide and drip with chlorine dioxide). Samples were quantified for indicator organisms using a most probable number technique, and analyzed for Escherichia coli O157 and Salmonella presence.
Results: Results represent the first season of a two-year study. Free-flowing surface water samples were lower in generic E. coli (1.6 log MPN/100ml) compared to samples with sediment (2.8 log MPN/100ml). Chlorine dioxide treatment in the irrigation line significantly (P < 0.05) reduced generic E. coli (<1.3 log MPN/100ml). Treated irrigation samples were lower (P < 0.05) than untreated samples at the point of application. E. coli O157 was detected from the irrigation line prior to chlorine dioxide treatment (1/13). One sample at the point of application (1/72) was positive for E. coli O157 (untreated, overhead). For harvest one, lettuce outer leaves (7/10) yielded E. coli O157 in treated and untreated drip and untreated overhead plots; no lettuce heads were positive (0/64). For harvest two, E. coli O157 was detected from lettuce head samples (2/64) associated with untreated overhead and drip irrigation plots.
Significance: Use of a chlorine dioxide water treatment system appeared to reduce generic E. coli levels in water, but influence on generic E. coli levels in the soil and lettuce and prevention of pathogen contamination was unclear.