Clearing Plant Life from around Produce Fields Doesn't Prevent Bacteria Contamination

Clearing Plant Life from around Produce Fields Doesn't Prevent Bacteria Contamination
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August 11, 2015

A university study suggests that clearing wild plants surrounding agricultural fields isn't helping to prevent bacteria from contaminating crops.

The study from the University of California, Berkeley calls into question the practice that began following a 2006 E. coli outbreak linked to packaged spinach that killed three people and made hundreds sick.

The outbreak was linked to one particular California farm and although E. coli was found throughout the farm environment – including in the feces of nearby cattle and wild pigs – the cause of the contamination has never been officially determined.

"Wildlife took much of the blame for that outbreak, even though rates of E. coli in wildlife are generally very low," study lead author Daniel Karp said in a statement. Karp is a NatureNet postdoctoral research fellow in UC Berkeley's Department of Environmental Science, Policy and Management and The Nature Conservancy.

With wild animals taking the blame, buyers began requiring the farmers create a clear buffer to deter wildlife from contaminating fields. Famers began clearing bushes, plants and trees that might serve as a habitat or food source for wild animals. Researchers found, however, that this practice not only diminishes wildlife habitats but has not prevented bacteria contamination.

There are many agricultural benefits to leaving the vegetation, said researchers.

Study author Claire Kremen also said in a statement that there is strong evidence that these natural habitats encourage wild bee populations and help the production of pollinated food crops. "There have also been studies that suggest that a landscape with diverse plant life can filter out agrichemical runoff and even bacteria," she said.

To gather data for the study,

The researchers analyzed about 250,000 tests of produce, irrigation waters and rodents conducted by industry and academics from 2007 through 2013. The tests were conducted on samples from 295 farms in the United States, Mexico and Chile, and targeted the presence of pathogenic E. coli, Salmonella and generic strains of E. coli. The researchers combined the test data with a fine-scale land-use map to identify characteristics of the landscape surrounding the agricultural fields.

Overall, the prevalence of pathogenic E. coli in leafy green vegetables had increased since the outbreak. Researchers found that growers who removed the most vegetation experienced the greatest increase in pathogenic E. coli and salmonella in their vegetables over time.

Animals aren't completely off the hook, though. The study did find that the likelihood of detecting E. coli was greater when fields were with 1.5 kilometers of grazeable land than when they were farther away. It's unclear whether those levels are caused by cattle or wildlife.

Study authors do believe farming and ranching can co-exist if proper systems are put in place. Researchers suggest leaving strips of vegetation between grazed areas and fresh produce areas. Vegetables that are usually cooked before being eaten can also be planted between grazing lands and fields that produce foods that are eaten raw. Fencing off upstream waterways from cattle to prevent waste from going downstream can also further prevent bacteria contamination.

More information and the full study can be found here.