May 2006. Can urea be used to reduce the concentration of glyphosate for controlling weeds? If so, what is the concentration to use?
The main purpose for adding urea or ammonium sulfate (recommended) is for acidification of the solution to enhance efficacy of the glyphosate. The recommended rate of glyphosate is not reduced. It is possible to add vinegar to achieve the same effect. A pH of 5.2 is desirable for the most effective use of glyphosate. This would be important in places that have “hard” (high pH) or near neutral water.
Other members said that urea was used to aid penetration of glyphosate into the foliage; whether it also reduced the time required for penetration, and hence reduced the rain-free period necessary after spraying, was not known.
A rate of 3 kg urea in 400 litre tank-mix of glyphosate was thought to be appropriate (although others said 1%).
It is important that glyphosate is sprayed early on a bright sunny day or, if dew is heavy, a little later. Clipping the plants to be sprayed, applying urea and then, later, glyphosate, is also an effective strategy, although it increases the work load considerably. Glyphosate is more effective when it is applied on rapidly growing plants.