Agriculture faces a set of major interrelated challenges in the 21st century: it must achieve global food security, meet high quality and safety demands, reverse degradation of ecological life-support systems, and respond to an ongoing biodiversity crisis. In California, we are evaluating how agriculture can be co-managed to simultaneously secure health, conservation, and food production outcomes. Recent outbreaks of shiga-toxin producing E. coli (STEC), Salmonella spp., and Campylobacter spp. in fresh produce have caused regulators and industry buyers to pressure farmers to change their practices. Many farmers no longer apply animal-based composts to their fields. Moreover, concerns that wildlife host diseases have led to the removal of seminatural vegetation around farms because it is thought to be wildlife habitat. After surveying ~600 California farmers, we found that 40% are removing vegetation due to food-safety concerns. Interviews with growers suggest many do not believe these practices make their food safer, but the pressure from buyers is simply too great to withstand.

Aligning with grower sentiment, our recent work suggests that animal-based composts do not enable pathogen survival. Instead, composts may promote beneficial bacteria that suppress pathogens. Similarly, we analyzed ~250,000 STEC and Salmonella tests from fresh produce collected across California’s Central Coast and found vegetation removal does not improve food safety. If anything, pathogens increased most on farms that had removed vegetation in the past.

Removing vegetation has far-reaching consequences for the environment and for farmers, beyond any impacts on food safety. We established a network of 27 organic strawberry farms in California’s Central Coast to study how diversifying (or homogenizing) agricultural landscapes affects multiple services and disservices from birds to farmers. Birds can benefit farmers by consuming crop pests, but may also eat beneficial insects, damage crops, or carry foodborne pathogens. We used point counts to measure bird diversity, exclusion experiments to quantify impacts of birds on strawberry yields, and mist nets to collect, sequence, and build diet profiles from bird feces. Though the net effects of birds on crop yields were fairly neutral, increasing seminatural vegetation around farms was associated with more diverse and multifunctional bird communities that provided more services and fewer disservices. As a result, the net impact of birds on crop yields was more positive on farms surrounded by more seminatural vegetation.

What about the food-safety risks from birds? After combining our pathogen data with other studies in the Western U.S. (~11,000 pathogen tests and 94 bird species), we found that Salmonella and STEC were very rare in birds (0.46% and 0.22% prevalences). Campylobacter was more common (8% prevalence), but actually tended to decrease on farms with more surrounding habitat. We are now extending this work in two ways. First, to better understand and manage food-safety risks from birds, we are creating the holistic food-safety risk assessments for birds by quantifying pathogen prevalences, bird defecation rates on farms, and pathogen survival in bird feces. Second, we joined an interdisciplinary team to study relationships between on-farm diversity, food safety, and soil health across lettuce farms in California. We aim to produce models that allow farmers, policy makers, and NGOs to evaluate how incentives and supply-chain requirements simultaneously affect farm profitability, food safety, and biodiversity.

News Coverage

Berkeley News, The Californian, Civil Eats, Cool Green Science 1, Cool Green Science 2, Daily Democrat, Deutschlandfunk, Food Quality News, Food Safety News, Monterey County Weekly, National Public Radio, National Sustainable Agriculture CoalitionObserver Press Chronicle, The Packer, Science News for Kids, TakePart, UPI, WKOW