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Marestail is a problematic winter annual weed that is often resistant to glyphosate. But control isn’t as hard as you think and just takes a little planning.

Marestail is a nuisance since it germinates in the fall, spring and early summer. Control is relatively easy even without glyphosate when application timing is right. And since it has such a wide germination window, it is important that control be well planned out in advance. The last thing you want to do is control marestail after it’s bolted since control is almost impossible.

One of the more common practices is to tank mix 2,4-D or dicamba with glyphosate as a burndown in the spring. However, because of the extended germination window, this practice is not totally successful in controlling this weed. Another option is planting a cover crop because it can suppress this weed and reduce the population of viable seeds in the soil.

In a 2010 study conducted by Ohio State University, soybeans yielded 51 bushels per acre when the burndown control failed, 57 bushels when burndown worked and 65 bushels when the burndown was stacked with a residual herbicide. The results emphasize the importance of adding in an appropriate residual herbicide when controlling marestail.

Ohio State University scientists Mark Loux at Ohio State University and Bill Johnson at Purdue University recommend a fall and spring burndown and a spring-applied residual program to control marestail for 6 to 8 weeks after planting. A fall program should be used in problem fields and where marestail seedlings are seen in the fall.

In a spring burndown use 2,4-D and combine it with dicamba, glyphosate, Sharpen or Verdict, Gramoxone, or use Liberty alone. The common cocktail of glyphosate and 2,4-D applied in the spring has become more variable for control of marestail. A post application is most effective when plants are no larger than the rosette stage at the time of application. Lastly, include a residual herbicide with the burndown treatment in the spring to gain another 6 to 8 weeks of control.

Dallas Peterson, Weed Management Specialist, and Doug Shoup, Southeast Area Crops and Soils Specialist at Kansas State University, wrote “Controlling marestail in the growing soybean crop can be the biggest challenge for producers. Glyphosate alone is often not effective on larger plants or glyphosate-resistant marestail. The most successful treatments for large marestail in Roundup Ready soybeans have been with combinations of glyphosate + FirstRate, glyphosate + Classic, or glyphosate + Synchrony. However, some marestail may also be resistant to Classic, FirstRate, and Synchrony and control may be marginal. If Xtend soybeans are planted, Xtendimax and Engenia should be some of the most effective herbicides for postemergence control of marestail in soybeans. Remember that Xtendimax and Engenia can only be applied to Xtend soybeans (and alone and not tank mixed). Another option to control marestail in soybeans is to plant Liberty Link soybeans and use Liberty herbicide. It is important to remember that Liberty can only be applied postemergence on Liberty Link soybeans.”

Read the full K-State Research and Extension article here.

Soybean agronomist Daniel Davidson, Ph.D. posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.