Basis for changes in glyphosate phytotoxicity to barley by the non‐ionic surfactants Tween 20 and Renex 36*

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Abstract
Summary: The non‐ionic surfactants, Tween 20 (polyoxy‐ethylene 20 sorbitan monolaurate) and Renex 36 (polyoxyethylene 6‐tridecyl ether) enhanced the retention of a glyphosate‐dye spray solution by barley (Hordeum vulgare L.) leaves. Tween 20 also enhanced absorption of 14C‐glyphosate applied as droplets to barley leaves whereas Renex 36 similarly applied, reduced both absorption and movement of 14C‐glyphosate. Renex 36 alone or mixed with glyphosate increased leakage of electrolytes from barley leaf segments whereas neither Tween 20 nor glyphosate, alone or mixed together, had any effect. No 14C‐glyphosate complexes were detected in mixtures with either surfactant and neither surfactant affected the pH of the glyphosate solution. The results indicate that the reported enhancement of glyphosate phytotoxicity by Tween 20 is due to increased retention and absorption of the herbicide while the reported antagonism caused by Renex 36 is due to reduced glyphosate absorption and movement possibly as a result of alteration of membrane integrity.