Profitability and efficacy of soybean seed treatment in Michigan

Soybean (Glycine max Merr.) is a globally important oilseed crop. Use of seed treatments to avert yield loss by managing seedling pathogens, early-season insects, and nematodes has become more common. Seed treatments may effectively protect plant stand and plant health in the presence of pathogens and pests, but the profitability of prophylactic seed treatment use across diverse environments remains in question, particularly when pests and pathogen populations are low or absent. Seed treatments, including a non-treated control (NTC), fungicide (F), fungicide-insecticide (FI), and fungicide-insecticide-biological nematode protectant (FIN), were evaluated on four soybean varieties at seven field sites in 2013, 2014, and 2015. In 2013, yield data was collected, and in subsequent years additional parameters were measured. FIN significantly improved plant stand at two sites in 2014 and three sites in 2015. Scant soybean aphid (Aphis glycines Matsumura) numbers were found at four sites across 2014 and 2015. Soybean aphid populations in FI plots were lower relative to the NTC at two of the four sites. Soybean cyst nematode (Heterodera glycines Ichinohe) (SCN) was present in one field in 2015, but FIN treatment did not significantly reduce SCN reproduction or population relative to the NTC. Yield across soybean varieties was significantly improved by FIN at the Allegan county sites in 2013 and 2015. Across sites in 2013, no seed treatment significantly improved net returns relative to the NTC. Across sites in 2014 and 2015, FIN significantly reduced net returns relative to the NTC. The probability that a seed treatment would result in economically neutral or positive outcomes was estimated by using Maximum Likelihood Estimation. Results from these planting dates and seeding rates indicate that seed treatments may not benefit all soybean growers. Seed treatment benefits may be affected by soybean variety, soil, environmental conditions, planting population, and planting date. Early planting dates and reduced seeding rates may see an increase in seed treatment profitability.