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Influence of planting date, seed treatment, and cultivar on plant establishment, sudden death syndrome, and yield of soybean
Y. R. KANDEL (1), K. A. Wise (2), C. A. Bradley (3), A. U. Tenuta (4), L. F. S. Leandro (1), D. S. Mueller (1). (1) Iowa State University, Ames, IA, U.S.A.; (2) Purdue University, West Lafayette, IN, U.S.A.; (3) University of Illinois, Urbana, IL, U.S.A.; (4) Ontario Ministry of Agriculture Food and Rural Affairs, Ridgetown, ON, Canada

A two year study was conducted in Iowa, Illinois, Indiana, and Ontario in 2013 and 2014 to determine the effects of planting date, seed treatment, and cultivar on plant stand, sudden death syndrome (SDS), and grain yield of soybean. Soybeans were planted from late April to mid-June at around 15-day intervals, for a total of three to four plantings per site-year. For each planting date, two cultivars differing in SDS susceptibility were planted with and without fluopyram seed treatment. Effect of planting date on foliar SDS symptoms was inconclusive. Mid-May plantings resulted in higher disease compared to other planting dates in two site-years, early June plantings in three, and the remaining six site-years were unaffected by planting date. Root rot was higher in May plantings for most site-years. Resistant cultivars had lower disease than the susceptible variety in most site-years. Fluopyram reduced disease severity by 12.5 to 95.2% across the site-years, and increased yield nearly in all plantings and cultivars, with a maximum yield response of 1142 kg/ha. Plant population was reduced by fluopyram seed treatment and early plantings in some site-years; however grain yield was not affected by these reductions. Mid-June plantings yielded up to 30% lower grain than early May plantings. Based on this experiment, delayed planting was not useful for SDS management, but cultivar selection combined with fluopyram seed treatment can reduce SDS in timely planted soybeans. 

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