KTIC Radio Extension Corner: Marestail Issues in Soybeans

glyphosate-resistant marestail in soybeans

This is Dr. Nathan Mueller, your local agronomist for Nebraska Extension. It has been a challenging spring due to the frequency of rain that caused the soybean crop to get off to a late start. On top of that we added some weed issues in our soybean crop, specifically marestail also called horseweed this year.

Marestail can be a winter and summer annual. Therefore, it can emerge from late summer into fall and overwinter as a rosette or it can emerge in the spring from March into June. Typically, we see a more fall and early spring emergence pattern in east central Nebraska, however with environmental conditions this years we have seen it emergence during May and early June. Therefore, burndown applications which included 2,4-D or Sharpen in April did not guarantee a field free of marestail.

Some marestail populations in eastern Nebraska has evolved glyphosate and ALS-inhibitor resistance. As this point, effective post-emergence herbicide options are very limited in soybeans. For example, FirstRate can provide about 80% control of marestail on ALS-sensitive populations, while PPO-inhibitors such as Flexstar may provide about 70% control. A sequential application of Liberty will be effective in Liberty Link soybeans. It may bring some memories back, but I do have contact information for growers in and around Dodge County interested a crew that will walk soybean fields.

As you re-evaluate your herbicide program for marestail next year, here are some suggestions:

  1. Include 2,4-D in your burndown to add control and follow the preplant interval.
  2. Use soil-applied herbicides with good residual for later emerging marestail containing the active ingredients metribuzin (Sencor), suflentrazone (Spartan), or flumioxazin (Valor).
  3. And always scout your field so you catch issues early.

For more information, call me at 727-2775 or visit our local website at croptechcafe.org. Know your crop, know your tech, know your bottom line. This is Dr. Nathan Mueller, your local agronomist for Nebraska Extension on KTIC radio.

This radio message was modified from a recent CropWatch article written by Amit Jhala on Post-Emergence Herbicide Options for Glyphosate-Resistant Marestail in Corn and Soybeans

NOTE: Watch pre-harvest interval, growth stage limits, and crop rotation restriction times on late soybean herbicide applications. For example, FirstRate can only be applied up to 50% flowering, glyphosate up to the R2 growth stage (full bloom), and Flexstar has a 10-month rotational restriction for corn.


KTIC Radio Extension Corner: Marestail Issues in Soybeans
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