Agronomy •  2022-12-19

Controlling Waterhemp with a program approach

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With documented resistance to six herbicide groups, waterhemp is a big problem for soybean growers across Canada. While predominantly an issue in Eastern Canada, it’s a growing concern in Manitoba as well.

When growing Enlist E3™ soybeans, using a program approach means using pre-emergence residual herbicides (with different modes of action) followed by Enlist™ herbicides post-emergence. This application strategy is built on herbicide stewardship and sustainability, while achieving excellent waterhemp control. Here’s how it works.

The problem: Waterhemp grows rapidly and is highly competitive. It’s a prolific seed producer (250,000 to 1,000,000 per plant), its seeds germinate throughout the crop year, and it has great genetic diversity, which makes it highly adaptable and able to develop resistance.

Currently, most waterhemp populations in Canada carry resistance to two or more herbicide groups, including Groups 2, 4, 5, 9, 14 and 27, making herbicide selection more critical than ever. Overuse of any herbicide group will inevitably lead to weeds developing resistance to that group – continued overuse only encourages the problem to become worse.

Controlling waterhemp with the Enlist™ weed control system: Because waterhemp is so adaptable and competitive, it’s critically important to protect herbicide tools so that they remain effective for as long as possible. This means using trait and herbicide technology responsibly by observing good crop and herbicide group rotations, practicing early weed removal, using multiple modes of action, following label instructions and not cutting rates.

The Enlist™ weed control system includes Enlist E3 soybean varieties with tolerance to 2,4-D (Group 4) and glufosinate (Group 10), and two Enlist herbicide options that, currently, all waterhemp populations are susceptible to. Specifically, they are:

  • Enlist Duo™ herbicide a convenient proprietary blend of 2,4-D choline (Group 4 & 9) and glyphosate.
  • Enlist™ 1 herbicide a stand-alone 2,4-D choline formulation (Group 4) that can be tank-mixed with Liberty® 200 SN (Group 10) or glyphosate.

Both herbicides come with Colex-D technology for near-zero volatility and low drift so it stays where it’s sprayed.

The program approach: This is a two-pass system that multiple modes of action to effectively control waterhemp, both resistant and non-resistant biotypes, in Enlist E3 soybeans.

  1. Start with a residual herbicide at pre-emergence. Because waterhemp is so aggressive and constantly germinating, it is critical to begin with a pre-emergence herbicide application with some residual activity. It is also key to use a mode of action other than Groups 4, 9 or 10 so you can “save” these for the second pass.

    Growers in Eastern Canada should apply Diligent herbicide (Group 2 and 14) to control glyphosate resistant waterhemp and other common broadleaf weeds. Growers in Western Canada should apply a pre-seed soil residual Group 14 herbicide that is registered for use in soybeans. Early weed removal helps crop emergence and establishment, while the residual control helps keep weed competition at bay through critical early growth stages.

  2. Then use an Enlist herbicide at post-emergence. Now that your crop has had a strong start, keep the field clean by applying either:
    a) Enlist Duo (Group 4 & 9) for the convenience of both 2,4-D choline and glyphosate in one formulation, or
    b) Enlist 1 herbicide (Group 4) tank-mixed with Glyphosate (Group 9) and Liberty 200 SN (Group 10) for the flexibility to tank-mix and adjust the rates of glyphosate and glufosinate.

Keep in mind that waterhemp has an incredibly wide window of emergence, so it’s important to monitor crops often for newly emerging weeds. Enlist herbicides can be applied right up to full flower (R2) when glyphosate is used and up to R1 (beginning of flower) when glufosinate is used – an application window wide enough to control late flushes of waterhemp.

Key takeaways: Waterhemp is so aggressive and prolific that effective management nearly always requires a second post-emergence herbicide application. This is true even if the population has not yet developed resistance. Enlist herbicides are a critical tool enabling post-emergence control in E3 soybeans, without fear of off-target movement. The addition of Liberty 200 SN provides an additional post-emergence tool making Enlist E3 soybeans the most flexible system for managing waterhemp.

Lastly, because most waterhemp in Canada is resistant to one or more herbicides, it is critical to pay attention to the modes of action you use, to rotate them, to use multiple modes whenever possible and make them part of a robust integrated pest management program. It is the only way to preserve herbicide efficacy for as long as possible.