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Impact of Corn Herbicide Activation Requirements on Weed Management

April 22, 2021
Corn row at York, Nebraska herbicide trial

PRE: Lexar® EZ herbicide 1.5 qt/A + AAtrex® 4L herbicide 1 pt/A; POST: Lexar EZ 1.5 qt/A + Roundup PowerMAX® 27 fl oz/A.
Lexar EZ contains the active ingredient S-metolachlor. This is from a corn herbicide trial at the York, NE, Grow More™ Experience site in June 2020.

Herbicide activation is a key factor in weed management that can often be overlooked. With several weed management options available, it’s important to understand the different active ingredients – like acetochlor and S-metolachlorand how they activate to determine which herbicide best fits your needs. Here are some factors to consider:

  • Encapsulation: When a herbicide is encapsulated (covered by a protective coating made of polymer, plastic or starch) and remains that way through the application process, more moisture may be needed for activation and growers may experience reduced weed control due to a lower available dose.
  • Precipitation requirements: This is the amount of rainfall, or irrigation, required to activate the herbicide. This also depends on the existing soil moisture, soil type and organic matter present. These requirements are included in herbicide product labels.

Agronomy Service Representative Travis Gustafson explains the difference he saw between encapsulated and non-encapsulated active ingredients and their weed management effectiveness at the York, NE, Grow More Experience site.

Here is a summary of Gustafson’s findings when looking at encapsulated vs. non-encapsulated corn herbicides:

  • Encapsulated acetochlor-based herbicide brands (like Degree Xtra® and Warrant®) control weeds by inhibiting growth of seedling shoots. These brands need to be applied before weeds germinate, but since they are encapsulated when sprayed, they need enough rain (0.25-0.75”) within 7 days of application to break down and become active. Acetochlor provides control of most grass and broadleaf weeds, but only when activated. If they are activated by appropriate rainfall, these brands penetrate the soil at a lower dose and offer less control, which means a higher likelihood of weed escapes and the development of weed resistance.
  • We utilize encapsulation with S-metolachlor products in many of our corn herbicide premixes (like Acuron®, Lexar EZ, Lumax® EZ) to enhance formulation integrity. The key difference is that once in a spray solution, all of our S-metolachlor is released from the capsule and available for weed control of seedling roots and shoots. The built-in safener, benoxacor, provides crop safety so the active ingredients can start managing weeds as soon as the product is applied without fear of harming the crop. While rain is also required for activation of S-metolachlor brands, these herbicides need less moisture than acetochlor and offer longer soil residual activity and more control. S-metolachlor provides long-lasting and consistent management of annual grass and small-seeded broadleaf weeds.

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