Soil residual herbicide options after corn emergence
A compressed planting season can lead to situations where no soil-residual herbicide was applied to corn. Many, but not all, soil-applied corn herbicides can be applied after corn emergence. Products that must NOT be applied after corn emergence include Fierce, Sharpen, and Verdict. Severe crop injury can occur if these products are applied postemergence.
If postemergence application of a soil-applied residual herbicide is allowed, be sure to check the herbicide label for any crop height restrictions. Maximum height restrictions can range from 5 inch corn to 40 inch corn, depending on the product. A helpful table from the University of Illinois summarizes the maximum size corn can be for several of these products. In addition, be careful if you plan to use UAN as a herbicide carrier as UAN can enhance foliar activity of products. An article from Iowa State University discusses this concern and lists recommended maximum UAN rates based on crop stage.
Also note that most residual soil-applied products will have little if any activity on emerged weeds. A postemergence product may need to be added for control of emerged weed seedlings. As always, be sure to check the herbicide label for tank-mix restrictions and additive recommendations.