IS A RESIDUAL NEEDED WITH POST CORN HERBICIDES?
I have received a few calls about the need for residual activity with postemergence herbicide applications. Im going to focus on grass weeds, which were the basis for the calls. Of course, every situation differs. In some areas, weeds had emerged before it rained to fully activate preemergence herbicides. These fields may still get some benefit from the preemergence herbicides, but the escapes still need to be controlled. Other fields that are being treated entirely postemergence may have a greater need for residual activity as there was no residual herbicide in the system yet. Lets consider a crop planted on May 1 for an example. We would typically like to have 8 weeks of residual weed control provided by a preemergence herbicide. By that time (July 1), the corn should be canopied and shading out most weeds emerging during the rest of the season. Plus, weed germination is also greatly diminished by that time of the summer. If we are making a postemergence application on June 1, we nor
