Organic fields increase pesticide use in nearby conventional fields, but reduce it in organic neighbors

Expanding organic cropland can lead to increased pesticide use in surrounding conventional fields while reducing pesticide use on nearby organic fields, according to a study based in a leading U.S. crop-producing region. The findings provide insight into overlooked environmental impacts of organic agriculture and suggest that clustering organic fields could reduce pesticide use at the landscape scale. Organic agricultural practices are designed to have less negative local environmental impacts than other forms of intensive agriculture. However, the broader environmental and functional impacts of agricultural practices are only partially understood. By not using harmful chemical pesticides nor genetically modified seeds, organic cropland may function differently than conventionally managed fields, harboring more pest and beneficial species, or less. Some of these species may spill over into surrounding areas and affect pest control decisions for nearby fields. Using pesticide application data from nearly 100,000 observations from ~14,000 agricultural fields across Kern County, California – one of the leading crop-producing and pesticide-using counties in the U.S. – Ashley Larsen and colleagues evaluated how organic crop production influences pesticide use on surrounding organic and conventional fields. Larsen et al. found that organic fields can help reduce the use of pesticides in surrounding organic fields but increased their use in conventional fields. The level of pesticide use on conventional fields decreased the further away they were from nearby organic fields. By modeling the spatial configuration of different types of fields, the authors found that pests could be managed if organic and conventional fields were spatially segregated. When organic fields occupy a small share of acreage and are scattered across the landscape, expansion of organic farming increases overall pesticide use across the landscape. However, clustering organic fields close together lowers overall pesticide use on both organic and conventional farms by mitigating the spillover effects. Whether increasing pesticide use on conventional fields is due to spillover of pest species from organic fields or other farmer decision-making processes is unknown. “The analysis that Larsen et al. conducted documents how pesticide use can depend on the characteristics of neighboring farms, but it does not elucidate the mechanism that those patterns arise from,” writes Erik Lichtenberg in a related Perspective. “There is a continuing need for both ecological and economic fieldwork to elucidate the mechanisms at play.”

***A related embargoed news briefing was held at 11:00 a.m. U.S. ET on 19 March, as a Zoom Webinar. Video and audio recordings can be found here. The Science Advances paper mentioned during the Q&A is available here.***