Soybean yield response to plant distribution in Fusarium virguliforme infested soils

Sudden death syndrome (SDS), caused by the fungal pathogen Fusarium virguliforme, causes Significant yield reductions in soybean [Glycine max (L.) Merr.] in the United States. Appropriate recommendations to manage SDS for growers in Iowa and the Upper Midwest are limited. Th e research objective was to determine the response of SDS foliar disease incidence, severity, and yield to row spacing and seeding rate. In 2008 and 2009, at two Iowa locations, in fields with histories of SDS, SDS-susceptible and SDS-resistant cultivars were planted at 38- and 76-cm row spacing at seeding rates of 185,000, 309,000, and 432,000 seeds ha ^-1 in plots infested with and without the pathogen. Sudden death syndrome incidence and severity were very low; however, infested plots had greater SDS disease incidence and severity than uninfested plots. A row spacing × infestation interaction indicated 7% greater yield in narrow rows (38 cm) than wide rows (76 cm) in uninfested plots, with no yield advantage to narrow rows in infested plots. Soil infestation reduced soybean seed mass (7%) in narrow rows, explaining the yield reduction for narrow rows with greater SDS. Th e two highest seeding rates had increased SDS incidence but yielded 9% greater than the lowest seeding rate. Th e susceptible cultivar had greater SDS incidence and severity and yielded 7% less than the resistant cultivar. This study indicates that in infested plots with greater SDS symptom expression, the yield advantage of narrow rows may be negated; therefore, cultivar selection is crucial when planting in narrow rows to maximize yield.