In response to rising input costs and narrowing profi t margins, soybean [Glycine max (L.) Merr.] producers are continually looking for ways to increase soybean yield. One approach being promoted is the use of foliar fungicides, for both foliar pathogen control and nonfungicidal plant physiological eff ects. Th e objective of this fi eld experiment was to evaluate a strobilurin and a triazole alone or in combination on soybean in the absence of foliar diseases to determine the potential eff ect on soybean growth and yield. Th e experiment was conducted in Iowa at one location in 2005 and two locations in 2006 with four soybean cultivars. Triazole (tebuconazole), a curative fungicide and strobilurin (pyraclostrobin), a preventative fungicide, were applied alone and in combination at growth stages R1, R3, and R5. Low levels of foliar diseases were observed. Seed yield for the control treatment averaged 4308 kg ha −1 across all sites. Foliar fungicides did not aff ect soybean seed yield. Few diff erences were observed among the treatments in soybean growth and yield components. Total biomass was 10% greater with the pyraclostrobin applied at R3 compared with the control, and was a result of increased stem weight. In this study, fungicides applied in the absence of foliar disease did not produce nonfungicidal physiological eff ect or associated yield improvement. It was concluded that environmental conditions and assessment of disease levels should be used as a guide for foliar fungicide application on soybean.

Sudden death syndrome (SDS), caused by the fungal pathogen Fusarium virguliforme, causes signifi cant 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 fi elds 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. Th is 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.

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