Plan now to control marestail
By David G. Hallauer
Meadowlark Extension District Agent
Maybe the only good thing that came out of our 2012 weather was that in some places, fewer marestail were able to germinate and survive the winter. Still, it’s a huge challenge for no-till producers, and one that would appear by early scouting to be back with a vengeance for 2013.
Timing of application and weed size are critical factors when it comes to success—or lack thereof. Marestail germinates in the fall or early spring, so it’s up and going before we’re ready to plant soybeans. Control efforts must be initiated in a timely manner.
Kansas State University weed scientists Dallas Peterson and Doug Shoup suggest using a growth regulator herbicide like 2,4-D or dicamba in the early spring as an inexpensive and effective option to control rosette marestail. A residual herbicide can help with weeds that germinate between the fall and early spring burndown and soybean planting. Products that include Canopy EX, Classic, FirstRate, Sharpen, or Valor can help provide residual control against several broadleaf species including marestail. Consult labels for the required preplant intervals prior to planting soybeans.
By planting, marestail plants may have bolted, becoming more difficult to control. Burndown herbicides prior to planting include tank mixes of glyphosate with FirstRate, Classic, Sharpen, Optill, or 2,4-D (2,4-D labels ahead of soybeans have plant-back restrictions from 7 to 30 days). Sharpen is a relatively new herbicide that has provided good marestail control and can be applied any time before soybean emergence. Maximize marestail control by applying Sharpen in combination with methylated seed oil and at spray volumes of 15 gallons per acre or more.
For a rescue burndown to bolting marestail prior to planting, consider Liberty. It’s been one of the most effective herbicides to control bolting marestail and also has broad spectrum non-selective activity on other broadleaf and grass species if treated at a young growth stage. A contact herbicide, use a spray volume of 15 gpa or greater for the most consistent weed control. Liberty tends to work best under higher humidity and warm sunny conditions at application.
Control in the growing soybean crop can be the biggest challenge. Glyphosate alone is often not effective on larger 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. Another option to control marestail in soybean 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.