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Glyphosate + 2,4-D Compatibility – Part 1 (6/29/17)

Question: What causes glyphosate + 2,4-D to ‘set-up’ in the sprayer and plug screens and nozzles? Is it just a freak thing that happensoccasionally? It happened two times this week. One of the guys is just dumping his right in the top of the tank. They are putting the glyphosate first then adding the 2,4-D separately, so they are not touching in the cone. The AMS was added last.

Glyphosate + 2,4-D Compatibility – Part 1

Question: What causes glyphosate + 2,4-D to ‘set-up’ in the sprayer and plug screens and nozzles? Is it just a freak thing that happensoccasionally? It happened two times this week. One of the guys is just dumping his right in the top of the tank. They are putting the glyphosate first then adding the 2,4-D separately, so they are not touching in the cone. The AMS was added last.

Answer: This is called physical incompatibility. Salts of glyphosate and 2,4-D each can dissociate and bind with each other. For example, the K+ cation from the K salt glyphosate can disassociate from the glyphosate and dimethylamine (DMA) salt can disassociate from the 2,4-D anion. These four ions (glyphosate, K, 2,4-D, and DMA) are able to recombine.                                                                                                                                         

Binding of the K+ cation with 2,4-D results in a very low solubility product which readily precipitates out. This precipitation is worse when very low rates of water are used (low gpa) and when the temperature of the water is cold.

2,4-D-amine is more compatible with glyphosate-IPA (the original formulations of Roundup).

It is preferred to mix 2,4-D esters or 2,4-D acids with K salt glyphosate formulations. Esters do not disassociate, so no precipitate is formed and with the 2,4-D acid, the disassociated ion would be H+ which does not precipitate.

Rich Zollinger

Extension Weed Specialist

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