Weeds in Mississippi
Do I need a residual herbicide with Roundup Ready crops?
Previously, Monsanto had marketed the Roundup Ready system as a stand-alone program, however, the onset of Roundup-resistant (i.e. glyphosate) weeds has changed that mind set. By continually applying glyphosate multiple times during a growing season and over consecutive years some plant species have become resistant to this chemistry. There are currently five weed species documented as being glyphosate-resistant in Mississippi with those weeds being Italian ryegrass, palmer amaranth, waterhemp, horseweed, and johnsongrass. Having just one of these weeds in a production system can complicate control options. Depending on the situation, a residual herbicide may be beneficial in controlling these weeds.
Residual herbicides can benefit producers in many ways. Once activated, a residual herbicide can offer several weeks of residual weed control during critical times of crop establishment and development. Residual herbicides can also hedge against inclement weather patterns where timely applications of a postemergence product, like glyphosate, are delayed or hampered. In extreme weed infestations, residuals can help reduce weed populations to more manageable numbers. Residual herbicides may also offer alternative herbicide modes-of-action (MOA) that may prevent the onset of resistance in weed populations to more commonly utilized herbicides like glyphosate. Consult the Mississippi Weed Control Guidelines for specific herbicides and crops.
As with any residual herbicide activation of the herbicide is imperative as most herbicides require at least 0.5” of rainfall for activation. Scouting fields to ensure that the herbicides were applied and activated properly is essential as weed escapes can be difficult to control if allowed to get too large.
While there are no silver bullets in weed control, a residual herbicide can be an effective tool in the management and/or prevention of glyphosate-resistant weeds.