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Wild vegetation and vegetable farming practices

Clearing wild vegetation surrounding vegetable crops may not be as good an idea as once thought.

When it comes to food safety, few stakeholders are more concerned about the spread of food pathogens than vegetable farmers. What farmer wants to be responsible for an outbreak of food-borne illness or face stiff penalties or litigation for failing to insure a high-quality, healthy food product?

But in an effort to improve safety on the farm, sometimes food safety experts and regulators come up with solutions and make recommendations to farmers that over time prove inadequate, and perhaps even contrary to the best farming practices.

For example, researchers at the University of California-Berkeley recently determined that clearing wild vegetation surrounding vegetable crops may not be as good an idea as once thought, citing a lengthy study that indicates the practice can be detrimental to preventing food quality issues.

The idea to clear wild vegetation surrounding crops came about in 2006 as a result of an outbreak of pathogenic E. coli in packaged spinach that caused the death of three people and sickened hundreds more. Following an investigation it was determined the outbreak originated from a California vegetable farm that supplied the lion's share of the country's fresh salad produce. The cause of the outbreak was never determined.

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Investigators found the disease-causing E. coli strain at multiple locations across the farm, but in spite of a lack of evidence that could pinpoint the exact cause, many theorized the outbreak may have been caused or spread by feces of both domestic and wild animals on or near the farm, specifically cattle, feral swine and rodents.

Wild vegetation removal

Following that incident, wholesale buyers of produce, mostly food distributors and grocery chains, pressured farmers to adopt the practice of removing wild vegetation from vegetable fields as a way discouraging cattle and wildlife from foraging near the fields. Considering no clear cause could be determined, many believed the idea was reasonable as an effort to minimize pathogen risks on the farm.

Nearly ten years later researchers at UC-Berkeley are suggesting the practice of and removal of wild vegetation on the farm may be causing more problems than solutions for farmers and consumers alike.

"There is strong evidence that natural habitats surrounding crop fields encourage wild bee populations and help the production of pollinated food crops," noted senior author Claire Kremen in the new study. "Some studies suggest a landscape with diverse plant life can also filter out agrichemical runoff and even bacteria."

The study further indicates that changing the dynamics of wild vegetation on the farm can increase the risks of food safety.

The six year study involved testing produce, irrigation water and rodent activity by industry and academic researchers. In all, some 250,000 tests were conducted before the study was released. The findings were published last week (Aug. 10) in the journal Proceedings of the National Academy of Sciences.

According to researchers, removing non-crop vegetation from the testing area led to extensive loss of habitat "that is globally important for food production and natural resources."

The study concluded that removal of riparian or other vegetation failed to lower detection of pathogens in produce, irrigation water or rodent populations and the prevalence of pathogenic E. coli in leafy green vegetables had increased. It noted the grower who removed the most vegetation experienced the greatest increase of Salmonella in the crop over time.

"Clearing surrounding vegetation is a costly, labor-intensive practice that threatens wildlife habitat," said study lead author Daniel Karp, a NatureNet postdoctoral research fellow in UC-Berkeley’s Department of Environmental Science, Policy and Management and The Nature Conservancy.

The study also concluded that since removing vegetation fails to improve food safety, there is no reasonable basis or support in continuing the practice.

Alternative measures

The study did offer alternative measures to help reduce pathogenic E. coli in vegetable operations. They include:

  • Fencing off upstream waterways from cattle to prevent waste from going downstream.
  • Planting crops that are usually cooked before being eaten, such as corn, artichokes and wheat, between fresh produce fields and grazed lands.
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