Clark Brenzil, provincial weed control specialist with Saskatchewan Ministry of Agriculture, reminds farmers and sprayer operators that adding micronutrient solutions, especially zinc, to glyphosate is highly antagonistic to the herbicide. Other micronutrient ions that cause antagonism to glyphosate are calcium, magnesium, manganese and iron.
Brenzil says zinc seems to be gaining popularity again as a remedy for reducing the risk of herbicide injury.
Monsanto comment: We have never supported adding micronutrients to Roundup because of antagonism and loss of efficacy. If farmers want to apply a micronutrient, it should be done in a separate pass.
Brenzil also says micronutrients added to the sprayer tank can also cause poor solubilization of solubag technology used for some dry herbicide formulations and result in plugging of the screens and nozzles.