In a study published in Science, L. Claire Powers and colleagues from the University of Colorado Boulder, USA, analysed pesticide application data from 14,000 fields in one of the most agriculturally productive regions of the USA: Kern County, California. Quantification of the direct and spillover effects of organic cropland to neighbouring fields revealed that for every 10% increase in organic cropland area, pesticide use in neighbouring conventionally cropped land increased by 0.3%. By contrast, the implementation of organic practices was found to decrease overall pesticide levels of neighbouring organic farms (specifically, promoting reductions in insecticide usage). Simulation of insecticide use under increasing proportions of organic cropland revealed that to mitigate the negative effects of reduced pesticide use to adjacent conventional croplands, organic fields should be clustered together and spatially separated from conventional cropping systems. Although the data from this study are region-specific, additional analysis revealed that the trends observed in Kern County may be generalizable across the USA.
As has been observed many times in agriculture, biological interventions can have unintended consequences. Analysis of the implications of organic cropland expansion beyond the field level highlight the kind of knowledge gaps that could limit the positive effects of organic agriculture on reducing pesticide usage. Integration of this understanding of pest spillover effects and mitigative clustering strategies into sustainable agricultural policies will ensure that we avoid the negative consequences of organic expansion — at least the ones of which we are aware.
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