When Foliar Pyraclostrobin Fungicide Applications Can Produce Profitable Soybean Yield Response?.

During 2005 and 2009, 282 on-farm evaluation trials were conducted in soybean fields across Iowa to identify when a foliar application of pyraclostrobin produced profitable yield responses (YR). Because of a delay in plant maturity, 218 trials exhibited a fungicide-induced greening effect documented using the late-season color infrared (CIR) digital aerial imagery of the soybean canopy. These 218 trials were about 30% more likely to produce profitable YR (65% vs 35%) than those without the greening canopy effect. In addition, larger yield responses were observed in trials that received more than 30 cm cumulative March through May rainfall. We speculate that pyraclostrobin applications at R3 growth stage may have helped plants with poorly developed root systems from the excessive soil moisture during wet springs. Site-specific observations of spring rainfall can be potentially used to identify fields that most likely produce above break-even YR, and therefore, avoid unnecessary foliar fungicide applications on soybean.