In 2006, a deadly E. coli O157:H7 outbreak in bagged spinach was traced to California’s Central Coast, where >70% of the United States’ salad vegetables are produced. Though no definitive cause for the outbreak could be determined, wildlife was implicated as a disease vector. Growers were subsequently pressured to minimize wildlife intrusions onto their farm fields through removing surrounding semi-natural vegetation. Though the practice is now pervasive, effects of vegetation removal on foodborne pathogens and on ecosystem services that benefit growers remain unclear. We quantified changes in foodborne pathogens, lettuce pests, and natural enemies on farm fields throughout the Central Coast of California. First, we combined a fine-scale land-use map with three datasets comprising ~250,000 enterohemorrhagic E. coli (EHEC), generic E. coli, and Salmonella tests in fresh produce, irrigation waters, and rodents to quantify whether semi-natural vegetation surrounding farms is associated with on-farm pathogen prevalence. Second, we implemented a landscape-scale field experiment to assess how surrounding semi-natural vegetation affects the control of aphid pests on organic lettuce farms.
We found no evidence that habitat removal improves produce safety. While EHEC prevalence in produce was highest on farms near areas suitable for livestock grazing, EHEC, generic E. coli, and Salmonella did not increase near non-grazed, semi-natural areas. Rather, pathogen prevalence increased most on farms where non-crop vegetation was removed, calling into question reforms that promote vegetation removal to improve food safety. Additionally, we found that farms with surrounding semi-natural vegetation supported a diverse arthropod assemblage, whereas a herbivore-dominated arthropod assemblage occupied farms in simplified landscapes. Exclusion and sentinel prey experiments demonstrated that predatory arthropods consumed more herbivores at sites with more surrounding non-crop vegetation and reduced aphid pest infestations in lettuce. Our results suggest a path forward for co-managing fresh produce farms for food safety and environmental quality, as federal food-safety reforms spread across ~4.5M acres of United States farmland. Advancing a multifunctional vision for food-safety management could benefit farmers by increasing pest control without compromising food safety.