Palmer Amaranth: Don’t Skimp on the Soil-Applied Herbicides

Mark VanGessel, Extension Weed Specialist;

If Palmer amaranth is a weed in your fields or in close proximity, you need to plan on using a soil-applied herbicide. But that alone is not enough. You also need to:

  • Apply those products close to planting time. Applying soil applied herbicides 10 days before planting soybeans often leads to significantly less Palmer amaranth control when evaluated at harvest than if the herbicide was applied right after planting the soybeans.
  • Use the full labeled rate. Reduced rates result in a shorter period of control and often lead to less weed control at harvest.

Assume you will need a postemergence herbicide application. Since most of the Palmer amaranth is resistant to glyphosate and group 2 herbicides, options for control are very limited. Products containing fomesafen have been the most consistent for postemergence control since it provides both contact activity as well as residual control. However, the rate of fomesafen needs to be at least 0.3 lbs active ingredient or the equivalent of 1.25 pts of Reflex.