Effects of weed management practices on enteric pathogen transfer into lettuce (Lactuca sativa var. capitata)

We evaluated the effect of using farmyard manure (FYM) in combination with four weed control techniques on the hygienic quality of lettuce. Treatments with six replications included the application of fresh FYM on the soil combined with hand-hoeing (assumed high-risk) and fresh FYM incorporation combined with plastic mulch (assumed low risk). The experiment was repeated twice per season over two years at Bonn University, Germany. The amounts of enteric bacteria in all treatments were within the acceptable limits. Enterococcus was detected in the majority of the samples in concentrations up to 3.7 log10 CFU/g. The Escherichia coli contents of lettuce ranged between n.d. and 103 CFU/g. There was no consistent effect suggesting a specific risk linked to one of the experimental treatments. We conclude that weeding techniques did not increase the risk of exposure to E. coli when FYM is used for fertility in organic production systems.