Efficacy of Non-Ammonium Sulfate Water Conditioning Adjuvants

Abstract

Glyphosate is a weak acid herbicide and can bind with antagonistic salts in aspray carrier. Diammonium sulfate (AMS) is commonly used with glyphosate to enhance activity and overcome antagonistic salts. Dicamba-resistant soybean technology will restrict the use of AMS with dicamba because of increased herbicide volatility. The procedures used in these studies were based on previous studies conducted in 2010 and reported at the Thirty-First ASTM Symposium on Pesticide Formulation and Delivery Systems. Studies were conducted in 2015 in North Dakota, Indiana, Illinois, and Kansas to evaluate weed control from glyphosate (no adjuvant formulation) applied with non-ammonium sulfate (AMS) water conditioning (WC) adjuvants in distilled water and water with 1,000 ppm hardness. WC adjuvants were applied as recommended at 0.4 % to 1.25 % v/v and compared to treatment standards. Velvetleaf exhibited high herbicide antagonism from minerals, and antagonism was reduced or eliminated by AMS and some WC adjuvants. Several other broadleaf species showed responses to AMS and WC adjuvants that were similar to that of velvetleaf. WC adjuvants tested at multiple locations provided a high degree of treatment precision. Several WC adjuvants partially overcame mineral antagonism but did not provide a level of bioefficacy equal to that of surfactant plus AMS. Dipotassium phosphate (DPP) provided the greatest phytotoxicity, and adjuvants that contained DPP or additional surfactant (or both) resulted in the greatest control. The results from these studies should be beneficial in developing and approving an ASTM standard for water conditioning agents.