A common progression for farmers in the Roundup Ready crop system has been to gradually increase the rate of glyphosate as inconsistent weed control is observed. Thus, previous failed applications of glyphosate are followed with higher rates of glyphosate in subsequent applica-tions. There are multiple concerns with this approach. First, the use of a single herbicide until failure allows weeds to continue growing with the crop which can reduce crop yields. Even if a successful rescue treatment controls all the surviving weeds the span of time for the failed glyphosate application to the rescue treatment is significant enough to reduce crop yields. Second, the use of glyphosate in this manner has been implicated in the evolution of glyphosate-resistant weed biotypes throughout the U.S., which ultimately results in the loss of the most effective herbicide available for control of our primary weed species.
Soil Science Extension
University of Wisconsin Madison