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Investigation of E. Coli Survival on Contaminated Crop Residue


Our research team has conducted several in-field studies in the Salinas Valley and found
that if leafy green crops were exposed to E. coli either prior to emergence from soil or early in
their growth cycle, the plants at harvest were rarely contaminated and E. coli was rarely
recovered from soil or water. However, we found that if a mature spinach crop was
contaminated with E. coli and then disked into the field, we could recover E. coli from soil for a
much longer period oftime (over 85 days). <P>

We propose to investigate the dynamics of E. coli survival on lettuce residue
incorporated into soil. We will establish experimental plots in commercial field settings and
inoculate plants prior to disking. <P>
As treatments, we will employ commercial ground preparation
practices (multiple diskings, addition of irrigation water) and evaluate their effects on survival
and decline of E. coli in soil. Such experiments should provide the grower with practical
information on the duration of bacterial survival in soil and the role of post-harvest field
practices in reducing bacterial carryover. Because the research will be conducted in the Salinas
Valley, our results should reflect real world dynamics of the production environment in coastal

Koike, Steven
University of California Cooperative Extension, Monterey County
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