Ammonium Sulfate and Dipotassium Phosphate as Water Conditioning Adjuvants

Abstract

Glyphosate and dicamba are weak acid herbicides that can bind with antagonistic salts in the spray carrier. Ammonium sulfate (AMS) is commonly used as an adjuvant with glyphosate to enhance activity and overcome antagonistic salts. Dicamba use in resistant soybean will restrict addition of AMS due to the potential to form the ammonium salt of dicamba, considered more volatile than the applied form of dicamba, thus increasing risk of injury to nearby susceptible crops. Dipotassium phosphate (DPP) as a substitute for AMS does not contain nitrogen. DPP can partially overcome antagonism from minerals in the spray solution but is ineffective in reducing dicamba antagonism of clethodim. The margin of separation is greater on species that are particularly responsive to AMS in hard water. In addition to water conditioning properties of sulfate, ammonium in AMS increases herbicide absorption and translocation. The positively charged potassium from DPP is a weak herbicide antagonist and, even at low amounts, may reduce herbicide efficacy. Because DPP may condition water through the phosphate anion, the compound is void of nitrogen, which may explain why DPP does not exhibit the same level of overcoming mineral and herbicide antagonism as AMS.