How a Zero Tolerance Approach Can Minimize Weed Resistance

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Taking a zero tolerance approach is necessary to manage and control herbicide-resistant weeds, such as Palmer amaranth.

Herbicide resistance is becoming increasingly problematic, leading to yield and profit losses for growers throughout the United States. Despite increased awareness of resistance issues among growers, more herbicide-resistant biotypes are identified each year, making it more difficult to control weeds. Growers are doubling down on proper stewardship and implementation of multiple strategies for weed control to keep resistance in check. 


How did we get here?

Herbicide resistance is the result of overreliance on herbicides, especially those with a single site of action, as the only strategy to combat weeds. It is characterized by weeds that can survive after a herbicide application. These surviving weeds are known as biotypes. When poorly managed, biotypes reproduce and pass on the herbicide resistant trait to their seeds and add to the weed seed bank, causing problems for future growing seasons.i

The solution is not as simple as switching from one herbicide with a single site of action one year to another herbicide with a single site of action the next year. Over time, single biotypes can develop resistance to multiple sites of action. For example, a waterhemp population in Missouri was recently discovered to be resistant to six different sites of action.ii

Some weeds, such as waterhemp, are more likely to develop herbicide resistance due to their prolific nature - they produce a large amount of seeds per plant and have a high level of germination.iii

“When herbicide-resistant seeds perpetuate in the soil, the weed seed bank expands, just one weed per acre could result in more than a million weeds per acre next year,” said Mark Waddington, selective corn herbicides product development manager at Bayer. “Continually failing to prevent weeds from producing seeds could increase the prevalence of herbicide-resistant weeds, causing major problems for future generations. That’s why it is so important to take a zero tolerance approach that prevents weeds from producing seeds and minimizes further development of herbicide resistance.”


Take a zero tolerance approach to weeds

Take a zero tolerance approach to integrated weed management, preventing resistant weeds from going to seed by implementing a variety of well-planned strategies for maximum control.

1. Start clean

One key strategy for weed control is to start the growing season strong with clean, weed-free fields and keep them that way through canopy. “Cover crops and tillage can help ensure fields are clean at the start of the season,” said Waddington. “However, one of the best ways to start with clean fields is to use a pre-emergence, residual herbicide.”

With multiple sites of action and proper application timing, the first-pass, residual herbicide should be effective for killing weeds not yet out of the ground and controlling weeds that have already emerged. Eliminating weeds early in the season is one of the most important steps for season-long weed control.

2. Stay clean

Plan a second pass with a post-emergence herbicide application that takes weeds out when they are three-inches tall or less. This second pass is essential for taking out weeds before they produce seeds, so they are unable to leave behind traits of herbicide resistance in the weed seed bank.

3. Scout

If you notice any weeds that survived the herbicide application, identify and pull them before they go to seed to prevent escapes into the weed seed bank.

4. Prepare for harvest

A zero tolerance approach to weeds continues through harvest. It is always a good idea to make sure your equipment is clean to prevent the spread of resistant weeds into new fields. If you are aware of a field with known herbicide resistant weeds, harvest those fields last.

5. Plan ahead

Making a long-term herbicide plan is also important for taking a zero tolerance approach to minimize resistance. Plan two to five years out and incorporate multiple and different sites of action for maximum control of tough weeds.


Bayer solutions for weed management

To sustainably manage weeds, growers should implement a well-planned herbicide program that uses multiple sites of action, including one with residual activity for superior control of emerged weeds. Waddington recommends a two-pass program—Corvus®, followed by DiFlexx® DUO.

Corvus, tankmixed with atrazine, is a pre-emergence herbicide with three different sites of action that help growers minimize herbicide resistance and start with clean fields. With as little as one-half inch rain, its residual is reactivated for control of emerged weeds that lasts up to eight weeks.

DiFlexx DUO, tankmixed with a Roundup® Brand Agricultural Herbicide, is a postemergence herbicide that takes out tough-to-control weeds with three unique sites of action to minimize the development of resistance. It can be applied up to the V10 stage to halt late-season weeds before they go to seed. 

The two-pass herbicide program of Corvus, tankmixed with atrazine followed by DiFlexx DUO, tankmixed with a Roundup® Brand Agricultural Herbicide, has six distinct and powerful active ingredients to enable proactive resistance management tailored to combat superweeds. This combination is especially tough on glyphosate-resistant weeds, as well as for general grass and broadleaf control. With multiple sites of action, this two-pass herbicide program takes a zero tolerance approach to weeds to reduce the weed seed bank and minimize herbicide resistance, protecting future yields and profitability.

To learn more about managing resistant weeds, visit the Bayer integrated weed management webpage.


©2018 Bayer Group. Always read and follow label instructions Bayer, the Bayer Cross, Corvus, DiFlexx, and Roundup are registered trademarks of Bayer Group. Atrazine and Corvus are Restricted Use Pesticides. Not all products are registered in all states. For additional product information please call toll-free 1-866-99-BAYER (1-866-992-2937) or visit our website at www.CropScience.Bayer.us. Bayer CropScience LP, 800 North Lindbergh Blvd, St. Louis, MO 63167.

Work Cited

i Battel, R. “How does herbicide resistance occur?” Michigan State University Extension, 2018. https://www.canr.msu.edu/news/how-does-herbicide-resistance-occur

ii Gullickson, G. “Scientists confirm first case of waterhemp with six-way herbicide resistance.” Successful Farming, 2018. https://www.agriculture.com/crops/soybeans/scientists-confirm-first-case-of-waterhemp-with-six-way-herbicide-resistance

iii Gunsolus, J. “Herbicide-resistant weeds.” University of Minnesota Extension, 2018. https://extension.umn.edu/herbicide-resistance-management/herbicide-resistant-weeds

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