Fresh produce has become a primary cause of foodborne illness in the United States. 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. The outbreak catalyzed far-reaching, system-wide reforms in agriculture, as buyers pressured growers to adopt strict new farming practices to ensure food safety, many of which target wildlife as a disease vector. In response, growers erected fences, deployed poison traps, and cleared vegetation to create wide “wildlife-free” buffers around their fields. From 2005 to 2009, ~13% of the remaining riparian habitat along the Salinas River was degraded or destroyed. Even though these practices are ongoing (Baur et al. 2016 California Agriculture), their efficacy and reverberating socio-ecological impact was not rigorously investigated (Karp et al. 2015 Bioscience).
Our work showed that removing habitat may compromise natural pest control services that benefit lettuce growers (Karp et al. 2016 Journal of Applied Ecology). We also combined three datasets comprising ~250,000 enterohemorrhagic E. coli (EHEC), generic E. coli, and Salmonella tests in produce, irrigation waters, and rodents to investigate the efficacy of habitat removal in mitigating pathogen contamination risks (Karp et al. 2015 PNAS). We found that habitat removal did not mitigate food safety risk. No pathogen was more prevalent on farms with more surrounding riparian or other natural vegetation. Rather, Salmonella and EHEC exhibited the strongest increases over time on farms that had cleared riparian and other natural vegetation in the past. These findings contradict widespread food-safety reforms that champion vegetation clearing as a pathogen mitigation strategy, and indicate that achieving both food safety and nature conservation goals in produce-growing landscapes may be possible.
Why habitat removal failed to mitigate pathogen prevalence is still unclear. Does habitat removal affect wildlife movements onto fresh produce farms? Which species are the most important vectors for foodborne diseases? Are there better strategies for managing food-safety risks? Recently, we received a grant from the Center for Produce Safety to synthesize the literature, identify on-farm practices that work for improving produce safety, and develop a simple tool for farmers to guide decisions. We hope to identify practices that help co-manage fresh produce farms for wildlife conservation and food safety (Fig. 1).
Fig. 1: Promising practices for co-managing food safety and conservation include: 1. planting low-risk crops between produce and pathogen sources (e.g., grazed lands), 2. buffering fields with non-crop vegetation to filter pathogens from runoff, 3. fencing upstream waterways from cattle and wildlife, 4. attracting livestock away from waterways with water troughs, supplement, and feed, 5. vaccinating cattle, 6. creating treatment wetlands near feedlots operations, 7. reducing agro-chemical applications to bolster bacteria that depredate and compete with E. coli, 8. exposing compost to high temperatures, and 9. maintaining diverse wildlife communities with fewer disease hosts. Illustration: Mattias Lanas & Joe Burg.
Our Center for Produce Safety grant will also provide scope for developing new practices. For example, postdoctoral scholar Naresh Devarajan is using the long-term soil manipulation experiment at the Russell Ranch Sustainable Agriculture Facility to explore whether poultry compost and cover crops can benefit soil microbes that compete with and suppress foodborne pathogens. Identifying particularly suppressive bacteria, and how to increase their abundance on fresh produce farms, represents a viable path forward for improving foods safety via conservation practices.
- Olimpi, E.M., P. Baur, D. Gonthier, D.S. Karp, C. Kremen, A. Sciligo, and K.T. De Master (2019) Evolving food safety pressures in California’s Central Coast region. Frontiers in Sustainable Food Systems 3:102.
- Baur, P., L. Driscoll, S. Gennet, and D.S. Karp. (2016) Inconsistent food safety pressures complicate environmental conservation for California produce growers. California Agriculture 70: 142-151.
- Jones, M.S., Z. Fu, J.P. Reganold, D.S. Karp, T.E. Besser, J.M. Tylianakis, and W.E. Snyder (2019) Organic farming promotes biotic resistance to food-borne human pathogens. Journal of Applied Ecology 56: 1117-1127
- Karp, D.S., R. Moses, S. Gennet, M. Jones, S. Joseph, L.K. M’Gonigle, L.C. Ponisio, W.E. Snyder, and C. Kremen. (2016) Farming practices for food safety threaten pest-control services to fresh produce. Journal of Applied Ecology 53: 1402-141
- Karp, D.S.*, P. Baur*, E.R. Atwill, K. DeMaster, S. Gennet, A. Iles, J. Nelson, A. Sciligo, and C. Kremen (2015) Unintended ecological and social impacts of food safety regulations in the California Central Coast. BioScience 65: 1173-1183.
- Karp, D.S., S. Gennet, C. Kilonzo, M. Partyka, N. Chaumont, E.R. Atwill, and C. Kremen. (2015) Co-managing agriculture for nature conservation and food safety. PNAS 112: 11126-11131.
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