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Researchers explore the many factors impacting the pH of dicamba spray mixtures

September 11, 2019

WESTMINSTER, Colorado - September 11, 2019 - The EPA now requires new dicamba formulations registered for dicamba-resistant crops to have a pH of 5.0 or higher because of volatility and off-target damage concerns. When it comes to applying spray mixtures under field conditions, though, how do you ensure that pH remains sufficiently high?

In an article written for the journal Weed Technology, researchers summarize studies to determine the pH effect of various commercial products used in dicamba-based spray mixtures - including dicamba formulations, glyphosate, drift retardant, ammonium sulfate and several pH modifiers. In each instance, the products were added to water with an initial pH of 4.6 to 8.4.
  • Factors Increasing pH. The team found that the BAPMA salt formulation of dicamba (Engenia) increased spray solution pH. In addition, all the pH modifiers they tested raised pH above 5.0 - the critical value on the latest dicamba application labels.

  • Factors Decreasing pH. Adding potassium salt of glyphosate to dicamba spray mixtures decreased pH by 1 to 2.1 units, which could have a profound effect on dicamba volatility. Isopropylamine salts of glyphosate produced similar results. Ammonium sulfate, which is commonly used to increase the activity of glyphosate, also decreased pH - but typically by less than 0.5 pH units.
  • Factors Producing Mixed Results. In contrast to BAPMA, diglycolamine formulations of dicamba plus the pH modifier VaporGrip™ produced a mixed response.
  • Factors with Little to No Impact. The drift retardant Intact had no effect on pH. Spray carrier volume and the mixing order of various pH modifiers had only limited influence.
"Though no direct efficacy or volatility measurements are made in our report, it is clear that having an accurate understanding of what is happening to spray mixture pH is foundational to the sustainable and environmentally responsible use of dicamba products," says Tom Mueller, Ph.D., lead author of the paper and a professor at the University of Tennessee.
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Full text of the article "Spray mixture pH as affected by dicamba, glyphosate, and spray additives" is now available in Weed Technology Vol. 33, Issue 4.

About Weed Technology

Weed Technology is a journal of the Weed Science Society of America, a nonprofit scientific society focused on weeds and their impact on the environment. The publication presents original research and special articles about weeds, crops and new technologies used for more effective weed management. To learn more, visit http://www.wssa.net.

Cambridge University Press

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