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Glyphosate Commercial Brands are Formulation, Surfactant Loading and Salt Specific (05/21/20)

Glyphosate Commercial Brands are Formulation, Surfactant Loading and Salt Specific You may have heard the mantra from Extension, use full glyphosate rates that will kill weeds. But what is the correct rate?

You may have heard the mantra from Extension, use full glyphosate rates that will kill weeds. But what is the correct rate? Glyphosate is sold under many brand names in today’s environment and at different recommended rates. This communication is to remind you of several differences between commercial brands that may impact the use rate and cost including:

  • Acid Equivalent per gallon
  • Surfactant loading
  • Salt formulation

Acid Equivalent (AE) is a measure defining glyphosate efficacy. Commercial glyphosate formulations range from 3 to 5 lb AE [or 4 to 6.1 lb active ingredient (AI)] per gallon. Glyphosate rate to control weeds (usually expressed as fluid ounces per acre) is adjusted depending on AE per gallon. AE may also affect the price per gallon so though you might initially pay less for products with a lower AE, you will likely have to apply them at a higher rate for effective control.

Adjuvants are compounds facilitating the action of glyphosate and are either included in the formulation or added with glyphosate in the spray tank. Branded glyphosate products may have no, partial, or full adjuvant loading. Unless prohibited by the product label, we recommend adding non-ionic surfactant with commercial glyphosate formulations at 1 qt per 100 gal water for full adjuvant load products, 1 to 2 qt per 100 gal water for partial adjuvant load products and 2 to 4 qt per 100 gal water for no adjuvant load formulations. Do not apply glyphosate brands formulated with surfactants (partial or full adjuvant formulations) to bodies of water because surfactant components are toxic to fish and other aquatic life.

Glyphosate chemically is a weak acid which equates to a weak negative charge. Salt is formed when glyphosate acid is added to a base that has a positive charge. The salt is disassociated at the site of action when product is absorbed within the plant tissues. Only glyphosate acid binds to the target enzyme and is responsible for herbicidal activities. The major salts in glyphosate products are potassium (K), isopropylamine (IPA), ammonium and trimesium. Different glyphosate salts have variable effects on stability in formulation, absorption, and translocation within the weed. However, researchers have not found noteworthy differences in weed-control attributed to glyphosate salt. Most reports suggest differences in weed control are inconsistent and do not support a single superior glyphosate-salt formulation.

 

Tom Peters

Extension Sugarbeet Agronomist

NDSU & U of MN

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