By Darren Hefty
If your farm is not using full scale tillage, chances are you’re fighting some marestail. It is primarily a winter annual weed, so spring tillage will normally wipe it out. The strategy for no-tillers, strip-tillers, and others has been to use a Roundup burndown in the spring. As marestail has become tougher for Roundup to control, a variety of cut-rate tankmix partners have been used with some success. However, today much of the marestail across the U.S. is completely resistant to Roundup. So now what?
If someone asks me about marestail control, I plan on getting absolutely nothing out of the Roundup. Chances are, Roundup alone may kill a few of the marestail, but for the most part, adding more Roundup is like adding more water in the tank. My point is you need to use a full rate of a separate herbicide to do the job on marestail.
What if I sprayed something on the marestail and it just burned off the leaves at the top and the weed eventually re-grew? The answer why this happened is simple. You didn’t apply the right product at the right time or you didn’t apply a high enough rate. It’s important to remember that if the marestail is big in the spring, it is most commonly a winter annual plant, meaning it got a start in the fall. If you’re trying to spray it in the spring, it will already have a big taproot and multiple growing points. To be successful, you need to kill every growing point. Your herbicide application will normally start killing the most active growing points at the top of the plant and work its way down until either the plant is dead or the herbicide runs out.
Herbicides to use this spring (keep in mind that larger weeds may require higher rates):
Ignite as a burndown or in LibertyLink crops is an excellent option and can be tankmixed with other herbicides for even more kick. I view 29 ounces of Ignite as a minimum rate.
Corn - My favorite choice for a pre-emerge burndown is a full rate of Verdict. Verdict contains a high rate of Sharpen (Kixor). Be sure to use the proper adjuvants, and you’ll be amazed by the speed of control. The dicamba products have always been decent, too. Status at the highest labeled rate provides the best control in-crop, in my opinion. Banvel at 16 ounces plus a surfactant provides the most economical control, but Status has better crop safety. 2,4-D is not a good spring option ahead of corn, either in-crop or as a burndown. Banvel is a safer burndown option, and it doesn’t cost any more per acre than 2,4-D. In-crop, 2,4-D is definitely too hard on corn, especially when that corn is worth $5 a bushel.
Soybeans - Sharpen is a good helper, but you can’t safely use the 2 to 3 ounces you’d need to take down marestail with Sharpen alone. Sencor is a nice option at rates up to 1/3 pound per acre. Sencor can cause crop response in sandy soils and high pH situations, so use caution. Authority First or Sonic are good options as pre-emerge products. Both contain FirstRate, which is probably your best choice for some in-crop help later. For that reason, you may save the FirstRate for in-crop help on late-emerging marestail and ragweed. Otherwise, you could use some Classic with a post-emerge application. The challenge in some areas of the country is marestail is becoming both ALS-resistant and glyphosate-resistant, so Roundup, FirstRate, and Classic can’t control it.
Wheat - Sharpen makes a great burndown product in front of grass crops like wheat. Use the labeled additives for your area to get the most activity out of it. In-crop is not normally a problem in spring wheat due to crop canopy.
A final piece of advice: DO NOT PLANT INTO EXISTING STANDS OF MARESTAIL THIS SPRING. Since marestail is one of the toughest weeds to kill in-crop, make sure you wipe it out before you plant.