Recent rains across Iowa have halted field work and may have interfered with planned preemergence herbicide applications in corn. Corn and weed growth, however, continues. In situations where the corn, and most likely the weeds, have emerged prior to application of a planned soil-applied herbicide program, there are still options available. Most preemergence corn herbicides also can be applied postemergence in corn. A few exceptions include Axiom, Balance, and Epic, which may only be used prior to corn emergence. Many of the herbicides that can be used postemergence do not provide the same level and spectrum of weed control as they would when used prior to weed emergence. Individual fields should be monitored after application to verify the level of weed control obtained. Some herbicides may cause corn injury when applied postemergence under certain conditions so it is a good general rule to wait until the corn has recovered from environmental stresses before making postemergence herbicide applications.

The table below contains information outlining the recommended growth stage and height restrictions for corn and weeds when using some of the commonly soil-applied herbicides postemergence. A few additional comments pertaining to the use of these products postemergence are also included in the table. Remember to always refer to the individual herbicide labels for additional specific information such as rate adjustments, tank mix restrictions, insecticide interactions, adjuvant requirements, and other precautions regarding the use of these products in early postemergence applications.

Growth stage, plant height, and other considerations for postemergence applications of typically soil-applied herbicides