Produce contamination reduction method effectiveness questioned

Findings question the effectiveness of removing non-crop vegetation to reduce field contamination of fresh produce by pathogens.

The practice started largely in response to a 2006 outbreak of E. coli in packaged spinach that killed three people and sickened hundreds. That outbreak was traced to a farm in California's Central Coast, a region that supplies more than 70% of the country's salad vegetables.

Researchers analyzed about 250,000 tests of produce, irrigation waters and rodents conducted by industry and academics from 2007 through 2013. The study can be found here​.

Tests were done on samples from 295 farms in the US, Mexico and Chile, and targeted presence of pathogenic E. coli, Salmonella and generic strains of E. coli.

Researchers found the removal of riparian or other vegetation did not result in lower detection of pathogens in produce, water or rodents.

Prevalence of pathogenic E. coli in leafy green vegetables had increased since the outbreak, even as growers removed non-crop flora.

Growers who removed the most vegetation had the greatest increase in pathogenic E. coli and Salmonella in vegetables.

However, the study found the likelihood of detecting pathogenic E. coli was greater when fields were within 1.5 kilometers of grazeable land than when they were farther away.

Daniel Karp, a NatureNet postdoctoral research fellow in UC Berkeley's Department of Environmental Science, Policy and Management and The Nature Conservancy, said growers are pressured by buyers to implement practices meant to discourage wildlife from approaching fields of produce.

“This includes clearing bushes, plants and trees that might serve as habitat or food sources for wild animals. Our study found that this practice has not led to the reductions in ​E. coli​ and Salmonella that people were hoping for."​

Researchers suggested leaving strips of vegetation between grazed and fresh produce areas, fencing off upstream waterways from cattle to prevent waste going downstream, planting crops usually cooked before eating - corn, artichokes and wheat - between fresh produce fields and grazeable lands.