Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on May 12, 2008. The information contained within may not be the most current and accurate depending on when it is accessed.
By Mike Owen, Department of Agronomy
Given the way the season has developed, the best intentions to apply an Early Preplant (EPP) herbicide application prior to corn planting has gone out the window and it appears that applying a preemergence (PRE) application immediately after planting is also becoming a slim chance. Thus, many who intend to use a soil-applied residual herbicide treatment in corn may be forced to make the application of an early postemergence (EPOST) to the weeds and possibly the corn.
Below is a table containing herbicide options available in corn modified from an article that appeared in the University of Nebraska CropWatch newsletter. The list likely does not include all options given the generic status of a number of these herbicide active ingredients.
The concern about the delayed PRE/EPOST herbicide treatment, regardless of whether or not residual products are included, is making the application soon enough to protect crop yield. It is typical that herbicides will kill weeds that are larger but often after potential yield has been lost.
Furthermore, some weeds (i.e. winter annuals) become extremely difficult to control as they grow larger and the potential for crop injury also increases as the crop gets larger. Thus, the best option is to make the residual herbicide application immediately after planting. If this is no longer an option, apply the treatment as soon as possible after planting.
Please recognize that some herbicides are registered for application EPOST to the crop but do not have POST activity on weeds. Also, many of these products can be applied to corn that is considerably larger than appropriate to protect the potential yield and weed control may be variable due to the uneven distribution of the spray on the weeds (the corn canopy interferes with the spray coverage).
Be sure to follow the label directions and understand the limitations of applications as the weeds and corn get larger. Also, it is highly unlikely that any of the EPOST treatments will meet expectations as a “season long, one pass treatment.”
Scout the fields prior to application and use the correct product to control the weeds that are present. Recognize that some of the labels are not clear about the size of weeds that may be controlled after they emerge.
Herbicide Options Available for Corn
1Severe injury may occur if Callisto is applied postemergence to corn that has been treated with Counter or Lorsban. Do not tank mix with any organophosphate or carbamate insecticide. Do not cultivate within seven days of application.
2Do not tank mix this product with any other herbicide when applied postemergence.
3Do not mix this product with complex fertilizer mixtures such as 10-34-0 or flowables. Use only water or liquid nitrogen carrier.
4Apply this product to Roundup ReadyTM corn only.
Mike Owen is a professor of agronomy with research and extension responsibilities in weed management and herbicide use.