Soybean is almost always part of a healthy crop rotation on corn-growing acres. Weather events such as derechos, hail, and drought can lead to downed corn plants and lost harvest, but there is also the negative impact of high densities of volunteer corn as a weed the following season if the weather events occurred after ear set. Volunteer corn in soybean has been recorded as one of the most yield-limiting weeds in a soybean crop. In fact, the University of Nebraska showed that as few as 3,500 volunteer corn plants per acre can reduce soybean yields by as much as 10%.1 Furthermore, volunteer corn is often found in clumps that are more competitive than single plants, and more difficult to control with herbicides (Figure 1). Soybean fields with large amounts of volunteer corn may encourage rootworm beetles to lay eggs in soybean fields causing rootworm feeding to occur when rotated back to corn.
Careful planning is necessary when making an herbicide selection to control volunteer corn in soybean fields. Depending on the trait package of the corn crop used, the next season’s volunteer corn could have resistance to one or more of the following herbicides: glyphosate, glufosinate, and quizalofop. To find the herbicide tolerance of the corn trait previously planted, search for: The Handy Bt Trait Table 2022.2 Additionally, in the case of glyphosate or glufosinate, make sure that the soybean product planted is tolerant to the herbicide you have chosen to apply to control volunteer corn in the soybean field.
Beware of herbicide antagonism. When tank mixing 2,4-D, dicamba or some Group 15 herbicides, the efficacy of Group 1 grass herbicides can be reduced. This control reduction may be offset by using the high end of label rates or applying the Group 1 herbicide alone up to 1 day before or 7 days after the antagonizing herbicide in a manner directed by the respective product labels. Using proper adjuvants, nozzle size, and ground speed as recommended helps improve control.
Don’t wait too long. Controlling volunteer corn before soybean plants reach reproductive stages is a must. Smaller corn is easier to kill and allowing corn to grow larger allows it to become more competitive with the soybean plants.
As always, read and follow label directions.
1Rees, J. and Jhala, A. 2018. Impacts of volunteer corn on crop yields. CROPWATCH. University of Nebraska-Lincoln. https://cropwatch.unl.edu/2018/impacts-volunteer-corn-crop-yields/.
2DiFonzo, C. (Michigan State University) 2022. The handy Bt trait table for U.S. corn production. https://cropwatch.unl.edu/2022/handy-bt-trait-table-updated-2022-corn/.
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.
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