Controlling Volunteer Corn in Soybeans

By Dwight Lingenfelter

As the soybean crops continue to mature, volunteer corn is rearing its head in some fields. Data from a few Midwestern universities shows that populations of volunteer corn can reduce soybean yields. University of Nebraska found that a volunteer corn density of 3500 plants/acre led to 10% yield reduction in soybean. Doubling the density to 7000 plants/acre led to a 27% yield reduction. South Dakota State University results were similar – a volunteer corn density of 5000 plants/acre resulted in a 20% yield reduction (12 bu/acre yield loss in 60 bu/ac soybean). In addition, it was noted that clumps of volunteer corn tend to cause more yield reductions in those areas as compared to scattered individual plants. Furthermore, volunteer corn attracts corn rootworms to that field which can further perpetuate insect problems if corn is rotated to that field next year. Regarding management, we assume that most of the volunteer corn is glyphosate- and glufosinate-resistant (Roundup Ready/LibertyLink) so we will not spend time going over all the options for killing the various types of volunteer corn. In general, the most logical choices to control volunteer corn in any kind of soybean are the post-grass herbicides (e.g., Assure II, Select, clethodim, Fusilade, etc.). Below are some rates to consider depending on the height of the volunteer corn:

Always include the necessary adjuvants otherwise control will be impacted. In most cases, this will require the addition of a crop oil concentrate (COC) or methylated seed oil (MSO). If crop injury is a concern, a nonionic surfactant (NIS) may be used in place of an oil with Select Max only. Keep in mind if you plan to tank-mix a broadleaf-specific herbicide, the rate of the grass herbicide may need to be increased to overcome possible antagonism.