Effect of Inorganic Salts on the Toxicity and Translocation of Glyphosate and MSMA in Purple Nutsedge (Cyperus rotundus)

The effects of several inorganic salts on the toxicity and translocation of nonradiolabeled and 14 C-radiolabeled MSMA (monosodium salt of MAA) and the isopropylamine salt of glyphosate [ N -(phosphonomethyl)glycine] following foliar applications to purple nutsedge ( Cyperus rotundus L. ♯ CYPRO) were evaluated. Salts of the monovalent cations NH 4 + , K + , and Na + and to a lesser degree the anion PO 4 generally resulted in increased toxicity of these herbicides. Salts of the divalent and trivalent cations Zn ++ and Fe +++ frequently reduced the activity of glyphosate and MSMA, whereas salts of the divalent Ca ++ ion caused little or no effect on activity. Salts of the anions Cl – , NO 3 – , CO 3 —- , and SO 4 – resulted in increased, decreased, or unchanged glyphosate toxicity as influenced by the associated cation. Translocation of the radiolabel of 14 C-glyphosate and 14 C-MSMA was increased by the addition of NH 4 Cl, while retention of the radiolabel within the tissue of the treated area was increased by the addition of FeCl 3 to the treated leaf surface.