Effect of fungicide seed treatments on Fusarium virguliforme infection of soybean and development of sudden death syndrome

Sudden death syndrome (SDS), caused by Fusarium virguliforme (Fv), is a major yield-limiting disease of soybean in North America. Infection of soybean seedling roots by Fv results in severe root damage; therefore, fungicide seed treatments could potentially reduce these early-season infections and reduce severity of foliar symptoms that typically occur later in the season. Multiple fungicide seed treatment combinations were evaluated for their effects on Fv infection, DNA concentrations in roots, soybean root development, and SDS development in the field, greenhouse and laboratory trials. Several seed treatments decreased root disease symptoms compared with the non-treated inoculated control in the laboratory assay, and the biological seed treatment, Bacillus pumilus, significantly decreased seedling development and increased SDS root disease compared with the non-treated inoculated control. In the greenhouse, Fv DNA concentrations in roots were reduced by a treatment combining mefenoxam + thiophanate-methyl + azoxystrobin + Bacillus pumilus + prothioconazole + fludioxonil compared with the non-treated control; however, the reduction in Fv DNA did not improve root growth or decrease SDS symptoms compared with the non-treated control. Field trials were conducted in Valmeyer, IL in 2008 and in Urbana, IL in 2008 and 2009. Seed treatments had no effect on the concentration of Fv DNA in soybean roots and had very little effect on root morphology. At the Valmeyer location, most seed treatments significantly decreased SDS symptoms compared with the control. In summary, no consistent, significant effects of the seed treatments evaluated in this study on SDS or Fv root infection were observed. Therefore, soybean growers should continue to utilize other practices for SDS management until new seed treatments with consistent efficacy in controlling SDS are available.