Lower commodity prices have growers monitoring their inputs more closely than in previous years. Soybean weed control is one of the areas that farmers have invested more money into due to increased weed pressure and herbicide resistance. With this increased investment, a question that arises is, “Do I need to control volunteer corn in my soybean fields?”

Volunteer corn enters a field through kernel loss during harvest. This kernel loss can be from corn head shattering, lodging or ear drop. Populations can be significant in fields that have had storm damage, excess plant stress, insect feeding, disease pressure or improperly adjusted combines.

South Dakota State University conducted studies in 2007 and 2008 to evaluate the potential yield loss associated with varying densities of volunteer corn in soybeans fields. They established volunteer corn densities ranging from 0 to 17,800 plants per acre and allowed the volunteer corn to compete with the soybeans for the entire growing season. The research concluded: A density of 5,000 volunteer corn plants per acre reduced soybean yields by approximately 20%. A population of 5,000 plants per acre equates to one plant every 3.5 feet of row.

Controlling volunteer corn in soybeans not only helps maintain yield, but also provides a rotation benefit to help control corn rootworm for the following corn crop. Allowing volunteer corn to grow within a field provides a food source for larvae to hatch in that field. Corn rootworm need to feed on the nodal roots of corn to survive, so without that food source they die. Corn rootworm beetle populations will also migrate to corn that is silking in soybeans, increasing the potential for egg laying in that particular field. This management tactic is not effective for western corn rootworm variant or northern corn rootworm extended diapause populations.

There are a number of effective herbicides on the market to control volunteer corn. Table 1 lists three of the most common herbicides used and their respective rates. It is important to control the volunteer corn at a smaller size not only to decrease the competition to soybeans, but also to decrease the rate at which a postemergence herbicide will have to be used. Delaying control methods also allows insects to feed on the volunteer corn for a longer period of time, complicating rotation strategies. Even though it may seem trivial to invest in volunteer corn control, there are economic benefits for the actively growing soybean crop and for the following crop as well.

Sources:
A. Jhala, B. Wright, P. Chahal. 2013. Volunteer Corn In Soybean: Impact and Management. University of Nebraska – Lincoln Crop Watch Archives. University of Nebraska – Lincoln. (Available online at: https://cropwatch.unl.edu/archive/-/asset_publisher/VHeSpfv0Agju/content/volunteer-corn-in-soybean-impact-and-management)

L. Stahl, B. Potter, J. Gunsolus. 2013. Control Volunteer Corn for Yield Protection and Corn Rootworm Management. University of Minnesota Extension Weed Management Factsheet. University of Minnesota. (Available online at: http://www.extension.umn.edu/agriculture/corn/pest-management/control-volunteer-corn-for-yield-protection-and-corn-rootworm-management/docs/UM-Extension-VolunteerCornFactSheet-2013.pdf)

J. Alms, M. Moechnig, D. Deneke, D. Vos. 2008. Volunteer Corn Effect on Corn and Soybean Yield. Abstracts Volume 63. North Central Weed Science Society. (Available online at: http://ncwss.org/)