Four Strategies for Managing Marestail

A young marestail weed
A young marestail weed.

Marestail may commonly be known as horseweed, but it is nothing to horse around about. This noxious weed is native to North America and is common throughout the United States, with known herbicide-resistant populations in 25 states.i

Lambsquarters closeup on ground

Marestail weed at flowering stage

It is a tough, annual broadleaf weed that can significantly reduce yields in your corn fields.

Marestail can grow to be three-to-six feet tall with white and yellow flowers that are arranged in a branched cluster. The leaves on a marestail plant are linear and simple with entire or slightly toothed margins, and are arranged in an alternate pattern. Marestail is also characterized by its stems, which are erect and unbranched at the base of the plant.

The threat of marestail

Marestail has two periods of emergence: from late March through June and from late summer into fall. In the spring, seeds in the weed seed bank germinate as newly emerged weeds that will aggressively compete with the new crop for sunlight, water and nutrients. A pre-emergence herbicide application can help manage this competition in the spring.

In the fall, additional seeds will germinate. However, they may be too large for sufficient control with a spring herbicide application. Instead, fall emerging weeds can be managed with a herbicide application after harvest.

Managing marestail in both spring and fall helps reduce the weed seed bank. As a prolific seed producer, a single marestail plant can produce 200,000 seeds that can become part of the weed seed bank that collects at the end of the season.ii These potentially herbicide-resistant seeds can overwinter in the soil and germinate in future years, threating yields for seasons to come.

Strategies for managing marestail

“Growers should implement an integrated weed management program that incorporates a variety of strategies to manage marestail before seeds are produced,” said Mark Waddington, product manager for herbicides at Bayer.

Marestail is most easily controlled in the seedling or rosette stage before it reaches three inches tall.iii Waddington recommends four strategies for managing marestail in your fields:

  1. Tillage
    Mechanical practices, such as tillage, can help growers manage marestail by burying the seeds farther below the surface, making them less likely to germinate.
  2. Shade
    The practice of increasing shade in your fields restricts the amount of sunlight the weed receives. Without sunlight, marestail is less likely to thrive and survive in your fields. One method for increasing shade is planting cover crops. Cover crops can suppress marestail growth through competition for nutrients and preventing the weeds from getting sunlight. Narrow row spacing for quicker canopy closure can also increase shade in your fields and help limit marestail development.
  3. Herbicides
    Due to its semi-annual emergence patterns, marestail should receive a herbicide application in both spring and fall. In spring, it is important to use a two-pass herbicide program that includes a pre-emergence application with residual, as well as a postemergence application. After harvest, it is recommended to perform a fall burndown on your fields if marestail is present. With every herbicide application, it is important to use multiple effective sites of action to target marestail in multiple locations, minimizing its chances for survival.
  4. Scouting
    Take time to scout your fields and identify problem weeds throughout the growing season. If it is still early enough in the season, consider a herbicide application to target the problem weeds in your fields. If it is too late for an additional herbicide application, pull the weeds by hand before they produce any seeds that could add to the weed seed bank.

Bayer solutions for managing marestail

Take a zero tolerance approach to managing marestail to prevent any weeds from setting seeds. Waddington recommends a two-pass herbicide program of Corvus® Herbicide at pre-emergence, followed by DiFlexx® DUO Herbicide at postemergence.

Corvus (Groups 2 and 27), tankmixed with atrazine (Group 5), is a pre-emergence herbicide that helps you start with clean, marestail-free fields before the crop emerges. With as little as a half inch of rain, Corvus reactivates to provide superior control of emerged weeds.

DiFlexx DUO (Groups 4 and 27), tankmixed with a Roundup® Brand Agricultural Herbicide (Group 9), takes out tough-to-control weeds, such as marestail, at postemergence to keep fields clean all season long.

In addition to Corvus and DiFlexx DUO, the Bayer Herbicide Portfolio also offers a wide range of additional options for managing tough weeds like marestail, among others.

©2019 Bayer Group. Always read and follow label instructions. Bayer, the Bayer Cross, Corvus, DiFlexx and Roundup are registered trademarks of Bayer Group. Corvus is a Restricted Use Pesticide. Not all products are registered in all states. For additional product information, call toll-free 1-866-99-BAYER (1-866-992-2937) or visit our website at Bayer CropScience LP, 800 North Lindbergh Blvd. St. Louis, MO 63167.

Work Cited

i Sarangi, D. and Jhala, A. Marestail edging in on no-till crops. American Agriculturalist, 2017.
ii Sarangi, D. and Jhala, A. When is a Good Time to Scout and Control Glyphosate-Resistant Marestail?. University of Nebraska – Lincoln CropWatch, 2017.
iii GROW. Weed of the Week: Horseweed (Marestail). Getting Rid of Weeds Through Integrated Weed Management, 2017.

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