Paraquat Use As a Soybean Harvest Aid in the Southeastern U.S.: Developing Relationships between Timing, Yield, Seed Moisture, and Vegetation Index.

Harvest aids, or desiccants, are often necessary in properly timing the harvest of indeterminate soybeans when grown in the Southeastern U.S. However, little to no data exists to reconcile the restrictive label requirements for timing of paraquat herbicide as a harvest aid. According to the paraquat label the seed moisture must be below 30% moisture and at least 65% of pods must be brown, but this may not align with the maturity of the crop. The purpose of this experiment was to determine how the timing of paraquat herbicide as a harvest aid affected plant development, seed moisture, and yield. Two indeterminate varieties of differing maturities were planted under irrigated field conditions in 2019 and applications were made at three development stages (named Early, Mid, Late, corresponding to beginning R6, late R6, beginning R7, respectively). Spectral reflectance data was collected weekly using an unmanned aerial system (UAS), or drone, to determine if a relationship exists for predicting treatment effects on development stage, seed moisture, and final yield. Initial findings indicate only a moderate correlation between seed moisture content at the time of application and final yield. Plant maturity as evidenced by the calculated GNDVI values at the time of application offers a stronger correlation in predicting yield, and may indicate a wider degree of flexibility in timing of harvest aid application.