Reduced Grass Control with Postemergence Tank Mixtures

Mark VanGessel, Extension Weed Specialist;

Postemergence grass herbicides like clethodim (Select), sethoxydim (Poast), quizalofop (Assure II), and others are very effective for the control of emerged grasses. But, we know that tankmixing them with broadleaf herbicides can reduce the level of grass control. Recent reports have seen this when these postemergence herbicides are tankmixed with dicamba, 2,4-D, or glufosinate (Liberty). Increasing the rate of the grass herbicide can reduce the chance of this occurring, but it is not consistent. The best option is to make separate applications, particularly if the grasses are large.

Likewise, glyphosate is very effective on grasses, but when tankmixed with dicamba, 2,4-D, and glufosinate, reduced grass control can occur. Fall panicum, goosegrass, barnyardgrass, and johnsongrass are some of the species that seem to be most impacted by this antagonism.