Using Fluopyram Fungicide Seed Treatment for Control of Fusarium virguliforme and Increasing Soybean Yield.

Soybean [Glycine max (L.) Merr.] producers often delay planting in fields with known sudden death syndrome (SDS) pressure to reduce symptom development, thus functionally minimizing soybean yield potential and profitability.  A new commercially available fungicide seed treatment, fluopyram, has potential for allowing producers to utilize optimal planting dates while simultaneously reducing the impact of Fusarium virguliforme, the causal agent of SDS.  A two-year study was initiated in 2015 at three locations throughout Wisconsin (Arlington, Hancock, and East Troy) to examine interactions between planting date and seed treatment use on SDS symptom development and soybean yield.  The experimental design at Arlington and Hancock was a randomized complete block in a split-split-plot arrangement with four replications.  The main plot factor consisted of three target planting dates (May 1, May 20, and June 10).  Subplots consisted of a factorial of three seed treatments (control, clothianidin + Bacillus firmus, and clothianidin + Bacillus firmus + fluopyram) and two cultivars, and sub-subplots consisted of two inoculation treatments (non-inoculated and inoculated).  At East Troy, the design was a randomized complete block with four replications of the factorial of three seed treatments and two cultivars.  Plots were rated weekly for SDS incidence and severity from symptom development (approximately R5) up to R7.  Little symptom development was found at Arlington, with light to moderate symptom development was found at Hancock and East Troy, respectively. Fluopyram use did not interact with planting date to influence yield or SDS incidence, severity, disease index, and area under the disease progress curve (AUDPC).  Fluopyram use decreased SDS incidence, disease index, and AUDPC compared to the other two seed treatments at Hancock and East Troy.  However, a positive yield response, 330 kg ha^-1 (7%), from fluopyram use was only observed at the East Troy location.  While SDS development varied widely between locations, the 2015 preliminary results indicated fluopyram decreases SDS symptom development, but positive yield responses were only observed with moderate levels of SDS pressure.