Preventative pest management in field crops influences the biological control potential of epigeal arthropods and soil-borne entomopathogenic fungi

Field crop growers in the United States have adopted prophylactic pest management strategies to control sporadic crop pests that are spatially and temporally difficult to predict. While evidence shows these preventative management practices, specifically pesticidal seed treatments, can be important in regions with predictable pest pressures, employing them ubiquitously in field crops across the northeastern U.S. can have variable returns on productivity. Further, prophylactics may also limit the potential of integrated pest management (IPM). A three-year field experiment (2017–2019) was conducted in a maize-soybean cropping system to compare the influence of a preventative pest management practice and a scouting-based IPM practice on biological control organisms. Aboveground predator densities were measured via pitfall trapping and predation temporal dynamics were assessed using a standard sentinel-bait assay at two time points per year. Belowground biological control potential was determined using a sentinel-bait bioassay to quantify the abundance of soil-borne entomopathogenic fungi (EPF). The variable responses of beneficial communities to pesticide inputs were strongly influenced by season and time of application, underscoring the importance of applying pesticides only when necessary. Compared with no pesticide use, pesticidal seed treatments and foliar sprays together in a maize-soybean production system suppressed total predator activity-density, spider activity-density, predation, and infection potential of soil-borne entomopathogenic fungi in one out of three years of the field study. In the third year, the activity-density of spiders increased across all fields in preventative plots that included seed treatments only. Overall, the use of pesticides did not improve crop yield in either maize or soybean. These findings highlight that the use of a prophylactic pesticide program may not always be necessary for maximum crop productivity and that this management approach can occasionally have unintended negative consequences on above- and belowground soil biota and the ecosystem services they provide.