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Studies were conducted in 2009–2011 in ND, NE, KS, and IL to evaluate phytotoxicity from glyphosate (no adjuvant formulation) applied with commercial acidic ammonium sulfate (AMS) replacement (AAR) adjuvants in distilled water and in water with 1000 ppm hardness. Commercial AAR adjuvants were compared to AMS plus a nonionic surfactant (NIS). Most AAR adjuvants contain monocarbamide dihydrogen sulfate, which comprises sulfuric acid complexed with urea and will reduce spray water pH to approximately 2.0. This low pH is below the pKa of most herbicides and causes herbicides to have a neutral charge, which reduces binding with antagonistic cations in hard water. 1-aminomethanamide dihydrogen tetraoxosulfate (AMADS) at not less than 1 % v/v provided herbicide enhancement similar to that of AMS plus NIS in distilled and hard water. In the absence of hard water, some commercial AAR adjuvants enhanced glyphosate phytotoxicity in a manner similar to that of AMS plus NIS; however, in hard water, the glyphosate phytotoxicity was less. Generally, a rate of 1 % v/v was required in order for commercial AAR adjuvants to provide the same herbicide enhancement as AMS plus NIS. The AMADS concentration in commercial AAR adjuvants may be diluted with other ingredients in formulations. Lowering the spray solution pH did not increase glyphosate activity in hard water. Sulfate in AMS and AMADS can condition hard water, which might then allow the ammonium to enhance herbicide activity. AMADS applied at no less than 1 % v/v or AMADS contained in some commercial AAR adjuvants provides the minimum water conditioning from SO4=, similar to AMS. Hard water that is sufficiently conditioned with SO4= might allow urea in AMADS to enhance and optimize herbicide phytotoxicity, similar to AMS.
acidic water conditioner, adjuvants, glyphosate, ammonium sulfate
Zollinger, Richard K.
Professor, Dept. of Plant Sciences, North Dakota State Univ., Fargo, ND
Associate Professor, Dept. of Plant Sciences, North Dakota State Univ., Fargo, ND
Bernards, Mark L.
Assistant Professor, Dept. of Agriculture, Western Illinois Univ., Macomb, IL
Peterson, Dallas E.
Professor, Dept. of Agronomy, Kansas State Univ., Manhattan, KS
Young, Bryan G.
Professor, Dept. of Plant, Soil & Agricultural Systems, Southern Illinois Univ., Carbondale, IL