New Study Finds That Maintaining Diverse Vegetation on Farms Enhances Food Safety

A new study out of the University of California, Berkeley shows that removing vegetation adjacent to farms on California’s Central Coast has not reduced the incidence of E. coli found in fresh produce. Instead, the reverse is true: farms that retained nongrazed riparian or other natural vegetation types had significantly lower prevalence of generic E. coli in water and pathogenic E. coli in produce.

These results contradict the conventional wisdom that developed in 2006 when spinach contaminated with pathogenic E. coli entered the stream of commerce and caused three deaths and 205 illnesses. While the cause of this contamination incident was not conclusively determined, feral pig feces found near the field where the spinach was grown contained the same type of E. coli that contaminated the spinach.

Consequently, the produce industry adopted production practices that focused on eradicating vegetation adjacent to farms that might attract wild animals. Farmers also tore out riparian habitat in the belief it might house pathogen-carrying amphibians. The new study reports that land area covered by non-crop vegetation has decreased and bare ground has increased by 30% in the Salinas Valley.

But the new research indicates that this “scorched earth” approach has not enhanced food safety and shows that the removal of non-crop vegetation is ineffective in making produce safer.

The Berkeley researchers found that increased pathogen presence was more likely on farms from which farmers removed natural vegetation and expanded cropland, and also on cropland surrounded by grazeable land. Additionally, Salmonella in fresh produce was significantly associated with removing riparian vegetation.

Because organic farmers are required to utilize practices that conserve biodiversity on their farms, many common organic practices overlap with those recommended by experts to reduce on-farm pathogens. These practices include planting hedgerows and field borders, maintaining pollinator habitat, building soils with high levels of biological activity, and protecting riparian areas and wetlands.

The Berkeley research team suggests that feedlot operators, ranchers, and produce growers can all take additional steps to reduce food-borne pathogens. They recommend fencing waterways to keep out grazing animals, planting vegetative buffers between crop fields and grazed lands, and installing secondary treatment wetlands to absorb runoff from feedlots.

Source: Karp, D.S., S. Gennet, C. Kilonzo, M. Partyka, N. Chaumont, E.R. Atwill, and C. Kremen. 2015. Comanaging fresh produce for nature conservation and food safety. PNAS; published ahead of print August 10, 2015, doi:10.1073/pnas.1508435112. Download full article and supplementary information here.

For additional information on comanaging for food safety and on-farm conservation, consult A Farmer’s Guide To Food Safety And Conservation: Facts, Tips & Frequently Asked Questions, by Wild Farm Alliance and Community Alliance with Family Farmers.