Issue No. 12, Article 6/June 12, 2009
Maximum Corn Growth Stages for Postemergence Herbicides
The labels of most postemergence corn herbicides include application restrictions based on a maximum corn size (specified as corn height, leaf or collar number, or sometimes both). For product labels that indicate a specific corn height and growth stage, be sure to follow the more restrictive of the two. If these restrictions are not followed, there can be substantial crop injury that may lead to yield reductions. Adverse environmental conditions (such as prolonged periods of cool air temperatures) sometimes result in corn plants that are physiologically older than their height would suggest, so be sure to accurately assess plant developmental stage (i.e., leaf/collar number) in addition to plant height.
Table 1 details labeled corn growth stages for several postemergence herbicides. Keep in mind that maximum height restrictions may change when two or more products are applied in combination, so be sure to follow guidelines for the more restrictive corn stage to reduce the potential for adverse crop response.