Effect of Diluent Volume and Calcium on Glyphosate Phytotoxicity

The effects of diluent volume and calcium concentration on glyphosate [N-(phosphonomethyl] glycine] phytotoxicity were evaluated by adding 0.0, 0.0025, 0.005, 0.01, 0.02, and 0.04 M CaCl2to 1.68 kg/ha glyphosate and applying at 130, 190, 375, and 750 L/ha to tall morningglory [Ipomoea purpurea(L.) Roth] plants that were 10 to 12 cm tall. Thirty days after treatment, glyphosate phytotoxicity was reduced by calcium at diluent volumes of 375 and 750 L/ha. Addition of a sulfonine red dye to the spray solution showed that at 130 L/ha, runoff from tall morningglory leaves was negligible. At 375 and 750 L/ha different volumes, ½ to ¾ of the spray solution, as measured by dye retention, ran off the leaf surface. At 750 L/ha, the water and dye collected at the leaf margins and the spray pattern on the leaf surface was not uniform.