Spatially explicit models reveal rodents rapidly colonize soybean fields regardless of pre-planting chemical treatment timing for cover crop removal

Soybean (Glycine max) is among the most important field crops in the world, and the USA is a top global producer, but USA soybean losses have increased because of multitude of factors, including wildlife damage. Although small, terrestrial rodents (Order: Rodentia) are capable of causing substantial damage to soybean and other field crops. Consequently, methods need to be developed that can provide agricultural producers and wildlife managers with accurate information about rodent populations at the field-level. We conducted a multi-site, before-after-intervention study in the midwestern USA to evaluate the effectiveness of varying treatment timings for cover crop reduction/removal prior to soybean planting, which was previously posited as an effective non-lethal approach for reducing rodents in soybean fields and mitigating crop damage. We chemically treated cover crops immediately (control), at two-weeks, and at four-weeks in four fields prior to soybean planting and used hierarchical, spatially explicit models to examine the effects of treatment timing on rodent density from pre-treatment through post-emergence. The control, two-weeks, and four-weeks treatment timings resulted in 81%, 125%, and 189% average increases in rodent densities post-treatment. The number of unique individuals of each detected species also increased post-treatment for all three treatment timings. Thus, varying chemical treatment timing for reducing/removing cover crops prior to soybean planting may be an ineffective non-lethal approach for rodent population management in agroecosystems. Nonetheless, our study provides an illustrative example of an effective, multi-site methodlogy that could be used to reliably evaluate the status of rodent populations and the potential effectiveness of other rodent management methods.