By Mike Owen, Department of Agronomy
Given the recent bad weather, it is likely that a number of corn fields will be considered for replanting to soybean. However, before this is considered, two things must be resolved; first, how will you remove the existing corn stand and second, was there a residual herbicide treatment applied to the corn?
The first can be accomplished by a number of tactics including the use of glyphosate if the hybrid is not resistant to glyphosate, tillage, or the use of a graminicide. The latter may be more of a problem if one of the herbicides used has a rotational restriction that precludes replanting to soybeans. It is critically important that you know what was applied to the corn field and check the label to make sure that soybeans are a replant option.
While growers may rationalize that herbicide such and such (i.e. atrazine) was used at a low rate and that the amount of rain has likely lessened the potential for injury to the rotational crop, it is important to follow the label. In many instances, this type of rationalization will result in serious damage to the soybean crop.
Listed below are a few of the options that are available to control existing corn stands and the rotational intervals for replanting to soybean. Please note that these are only an overview and the specific label should be checked prior to any replant decision.
Table 1. Herbicides that can control existing corn stands
a Refer to the label for specific details
b Roundup PowerMaxTM used as an example – other glyphosate products may suggest different rates
Table 2. Rotational interval to plant soybeans for some herbicides used in corn
a This represents a partial list of products that restrict rotational crop option.
Refer to the specific herbicide label to determine if the product used has a replant rotational restriction.
Mike Owen is a professor of agronomy with research and extension responsibilities in weed management and herbicide use.
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