Integration of Host Resistance, Seed Treatment, and Seeding Rate for Management of Sudden Death Syndrome, a Disease of Soybean Caused by Fusarium virguliforme

Abstract

Field experiments were conducted in Illinois, Indiana, Iowa, Michigan, and Wisconsin, United States, 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 (foliar disease index [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. The base treatment included metalaxyl + pyraclostrobin + fluxapyroxad + clothianidin. The 2019 nontreated control and the 2020 base treatment were considered controls in the analysis because previous studies showed that base treatments do not provide control for sudden death syndrome. The seed treatments were tested on susceptible and moderately resistant (MR) cultivars, which were planted at three seeding rates: 272,277, 346,535, and 420,792 seeds/ha. To mitigate concern that disease pressure may impact treatment, three high disease pressure (>20% FDX) site-years out of the 15 total site-years were grouped and analyzed separately. 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, the MR cultivar had more RR than the susceptible cultivar. Additionally, FDX was only reduced in the MR cultivar in 2020. Although host resistance and seeding rate did not individually impact disease development and yield in every site-year, we showed that integrating seed treatment, host resistance, and adequate seeding rates helped maximize yield in fields with sudden death syndrome.