Based on the chemical properties of herbicide and carrier water, water hardness might have different impacts on herbicide performance. A study was conducted in the greenhouse to determine the effect of chloride and bicarbonate forms of Mg+2 and Na+ on the performance of clodinafop-propargyl and sulfosulfuron for littleseed canarygrass control. The concentrations of bicarbonate and chloride forms of Mg+2 and Na+ had no significant effect on the ED50 of clodinafop-propargyl. The relative potency of clodinafop-propargyl, in the presence of all mineral salts, was 1.0 or had no significant difference from 1.0. On the contrary, increasing the mineral salts reduced the ED50 of sulfosulfuron significantly, especially in the presence of bicarbonate forms of Mg+2 and Na+. In this regard, the relative potency of sulfosulfuron as affected by 100 to 800 ppm Mg(HCO3)2 was about 0.5 to 0.7 times higher than control. This value was increased from 0.5 to 2.2 at 100 to 800 ppm sodium bicarbonate. Hence, the ranking of the mineral salts on improving sulfosulfuron performance was NaHCO3 > Mg(HCO3)2 > MgCl2 > NaCl. It is suggested that because of the lipophilic nature of clodinafop-propargyl, the presence of mineral salts did not affect the performance of this herbicide. It is concluded that, in determining the effect of water hardness on herbicide performance, in addition to chemical properties of herbicide, type of mineral salt, and its concentration, it is also essential to know the changes in the pH of the carrier water due to the mineral salts.

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