Influence of fungicide on soybean seed quality from delayed harvest and environment

Field studies in 2019–2020 evaluated the influence of fungicide application on seed quality from delayed harvest (approx. 20, 30, and 44 days after optimum harvest timing, i.e., 13% seed moisture). Treatments included nofungicide, pydiflumetofen plus difenoconazole (13.7 fl oz/acre Miravis Top, Syngenta), or mefentrifluconazole plus pyraclostrobin plus fluxapyroxad (8 fl oz/acre Revytek, BASF). Effect of environment was investigated in both field (natural rainfall events) and environmentally controlled growth chambers (79°F or 90°F with 30% or 100% relative humidity and exposed for 48 or 96 h) for potential impacts on soybean [Glycine max (L.) Merr.] seed quality. Seed quality was based on a rating scale of 1 to 10 with 1 being seeds in good condition and 10 being seeds in poor condition, based on USDA reference images. Fungicide application had no effect on seed quality from delayed harvest or a saturated environment (100% relative humidity). Delaying harvest beyond approximately 20 days past optimum timing can result in reduced seed quality regardless of fungicide application (1.0 to 2.0 vs 4.0 to 8.1 rating). In addition, seedpod exposure averaged across temperature and relative humidity environments for as little as 96 h after optimum harvest timing can result in deteriorating seed quality issues (3.2 vs 1.4 rating) regardless of fungicide application. Results indicate that soybean harvest delayed 20 days after optimum timing and subjected to seasonal rainfall events or seedpods exposed to completely saturated conditions for 96 h associated with a tropical weather event will result in soybean seed quality deterioration regardless of fungicide application.