Issue No. 9, Article 2/June 1, 2012
Precautions with Postemergence Corn Herbicides
While applications of postemergence corn herbicides continue in many areas of the state, they are all but complete in other areas. As the corn grows, it's important to remember that the labels of most postemergence corn herbicides indicate a maximum corn growth stage beyond which broadcast applications should not be made. These stages are usually indicated as a particular plant height or leaf stage; sometimes both are listed.
For product labels that indicate a specific corn height and growth stage, be sure to follow the more restrictive of the two. For example, broadcast applications of glyphosate may be made through the 8-leaf collar stage or until corn reaches 30 inches in height, whichever comes first. Application restrictions exist for several reasons, but particularly important is the increased likelihood of crop injury if applications are made outside the specified growth stage or range. Be sure to consult the product label for specific information on maximum corn growth stages and whether the herbicide is labeled for directed application if the maximum corn growth stage has been exceeded.
Also, be cautious when applying growth regulator herbicides when corn is rapidly growing. Corn stalks can become "brittle" during periods of rapid growth and stem elongation, and these herbicides can enhance stalk brittleness.--Aaron Hager