Efficacy of neonicotinoid seed treatments of soybean under adverse abiotic conditions

Early season planting of soybeans, typically in April across much of the Midwest, has been identified as a critical approach for optimizing yields. However, this may increase the risks of losses to pests and diseases, leading producers to invest in prophylactic pest management approaches, including pesticide seed treatments, to minimize risk. Neonicotinoid seed treatments, such as thiamethoxam, are commonly used as insecticidal soybean seed treatments, along with a variety of fungicides. This study examines the uptake and translocation of these pesticides under the cold, wet soil conditions typical of early planting. We sought to test the hypothesis that abiotic factors influence pesticide concentration and distribution in soybean tissues both across time and within plant tissues. The study was conducted over two years (2023-2024) at three sites in Indiana. The study utilized a split-plot design with four treatments: CruiserMaxx APX seeds (thiamethoxam and four fungicides), thiamethoxam-only seeds, fungicide-only seeds, and untreated seeds. Soybeans were planted at four intervals, beginning in early April. Plant samples were collected at various early growth stages (VE to V4) and analyzed for pesticide residues using a modified QuECHeRs protocol. Soil moisture and temperatures were measured using Decagon 5TM sensors and loggers. Preliminary findings suggest that soil moisture and temperature significantly affect pesticide translocation. These results fill a critical knowledge gap of pesticide translocation within soybeans under cool, wet field conditions. As soybean early planting becomes more commonplace, these data can help inform production practices, and help optimize the deployment of seed treatments in the field.