Planting Date Effect on Soybean Sudden Death Syndrome Development and Yield Loss.

Delaying planting is a management strategy soybean producers can use to minimize symptom development of soybean [Glycine max (L.) Merr.] sudden death syndrome (SDS), caused by Fusarium virguliforme.  With the shift towards earlier planting dates for maximizing soybean yield and profitability, the impact of today’s optimal planting dates on SDS development and soybean yield loss are not yet well understood.  Field trials were established in Hancock, WI during the 2013 and 2014 growing seasons to investigate interactions between planting date and cultivar on SDS symptom development and soybean yield.  The experimental design was a randomized complete block in a split-split-plot arrangement.  Main plots consisted of three target planting dates (May 1, May 20, and June 10).  Subplots consisted of ten cultivars ranging in susceptibility to F. virguliforme, and sub-subplots consisted of two inoculation treatments (inoculated and non-inoculated).  In 2013, planting date × cultivar interactions were found for SDS disease index and area under the disease progress curve (AUDPC).  While disease levels differed among cultivars, results showed no difference between the May 1 and May 20 planting dates, but levels were significantly less for the June 10 date.  Highest yields were found in the May 1 planting date, and inoculated plots showed yield losses of 720 (17%), 770 (20%), and 400 kg ha^-1 (12%) for the May 1, May 20, and June 10 planting dates, respectively.  In 2014, planting date × cultivar interactions were found for SDS incidence, disease index, and AUDPC.  For each rating, diseases levels again differed among cultivars, but results showed highest disease levels in the May 1 planting date, with little disease observed in the May 20 and June 10 dates.  Yield losses in the inoculated plots were 400 (12%) and 270 kg ha^-1 (9%) for the May 1 and May 20 dates, respectively, but no difference was found in the June 10 date.  Although the early planting date (May 1) consistently exhibited the highest amount of SDS development, the results from this study suggest early planting coupled with good cultivar selection maximizes yield potential compared to delaying planting.