Evaluating the effectiveness of integrated strategies to manage sudden death syndrome of soybean: Supplementing SDS-resistant and -susceptible cultivars with chemical and biological seed treatments

Sudden death syndrome (SDS), primarily caused by Fusarium virguliforme, threatens soybean (Glycine max) production across the United States and Ontario, Canada. SDS thrives in cool, wet soils, with post-planting rainfall exacerbating disease, making pre-planting management strategies like resistant cultivars and seed treatments crucial. This study evaluated biological and chemical seed treatments on resistant and susceptible soybean cultivars across 14 locations in 2022 and 15 locations in 2023. Data collection included final stand counts, root rot severity, foliar SDS severity index (FDX), and yield. Trials were categorized into high (FDX ≥ 10%) or low (FDX < 10%) disease severity locations based on the non-treated control (NTC). In high disease locations, cultivar and seed treatment significantly (P ≤ 0.01) influenced FDX, root rot, and yield. The base+fluopyram and base+fluopyram+natamycin treatment reduced FDX by 6.7% and increased yield by 288.5 kg/ha over the non-treated. The resistant cultivar reduced FDX by 9.7% and root rot by 2.1%, while increasing yield by 247.7 kg/ha relative to the susceptible cultivar. Under low disease pressure, cultivar selection remained significant, with resistance reducing FDX by 2.4% and root rot by 0.8%, and improving yield by 445.5 kg/ha. In contrast, the effects of seed treatment were not significant in the low disease severity environments. No seed treatments reduced FDX or root rot and only base+fluopyram and base+fluopyram+natamycin increased yield (+254 to 301 kg/ha) compared to the non-treated in the low disease severity environments. Cultivar resistance remains the most effective SDS management strategy, with seed treatments providing significant benefits under high disease pressure.