Spray Solution pH and Glyphosate Activity

It was hypothesized 110 years ago that substances that dissolve in lipids pass more easily into cells than those that dissolve in water. Thus, weak acids such as glyphosate should more readily pass through the non-polar plant cuticle in the non-dissociated, more non-polar form. The objective of this study was to test this hypothesis in a series of studies in the greenhouse involving three weed species. The pH of the glyphosate spray solution was varied between 1.5 and 6. The glyphosate activity on giant foxtail, common lambsquarters, and velvetleaf (pH) was not affected by pH values between 1.5 and 6 when adjusted with hydrochloric acid (HCl). If diammonium sulfate, was also present, the results were similar; however, the glyphosate activity on velvetleaf was much greater. If the pH was lowered with sulfuric acid, H₂SO₄, an increase in the glyphosate activity on velvetleaf became evident as the pH was lowered from 6.0 to 1.5. This was attributed to the water conditioning effect of the SO₄⁼ in hard water. With tank-mixing glyphosate with 1 % NT