Integration of host resistance, seed treatment, and seeding rate for management of sudden death syndrome, a disease of soybean caused by Fusarium virguliforme

Field experiments were conducted in Illinois, Indiana, Iowa, Michigan, Wisconsin and Ontario Canada in 2019 and 2020 to evaluate the integrated effects of host resistance, seed treatment, and seeding rates on root rot (RR) and foliar symptoms of sudden death syndrome (FDX) and soybean yield. Seed treatments included a nontreated control and fluopyram in 2019. In 2020, commercial base treatment, base + fluopyram, and base + pydiflumetofen were tested. Base treatment included metalaxyl + pyraclostrobin + fluxapyroxad + clothianidin. Seed treatments were tested on susceptible and moderately resistant (MR) cultivars, which were planted at 272,277, 346,535 and 420,792 seeds/ha. Seed treatment with fluopyram or pydiflumetofen both reduced FDX and protected yield. Fluopyram reduced RR by about 10%, but RR was not different between pydiflumetofen and the base treatment in 2020. Both seed treatments reduced FDX, but reduction was greater for fluopyram (43.2%) than for pydiflumetofen (24.3%) based on 2020 results. Seeding rate had no effect on foliar symptoms, but the highest seeding rate showed increased RR in 2019, and greater yield both years. Performance of MR cultivars was inconsistent across both years. In 2019, MR cultivars reduced RR by 8.9%, however, in 2020, MR cultivar had more RR than the susceptible cultivar. Also, FDX was only reduced by the MR cultivar in 2020. Integrating seed treatment, host resistance, and adequate seeding rates helped maximize yield in fields with SDS.