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Volunteer corn competes with soybeans for space, water, nutrients and light. University studies show that 2.4 volunteer corn plants per 100 sq. ft. can reduce yield by 10 percent. Just six volunteer corn plants per 100 feet of row can also reduce soybean yields by as much as 10 percent. In addition to yield loss, volunteer corn makes harvesting difficult and causes both shattering and dockage.

Volunteer corn in soybeans is more commonplace today due to the adoption of the Roundup Ready^® trait in corn and soybeans and continual use of glyphosate. Now volunteer corn will just survive—often in large numbers.

Back in 2008, research released by Purdue University showed that volunteer corn also acted as a host of corn rootworm, helping it survive and reproduce in an off year, when you expect rootworms to starve and numbers to decline. Much of the corn planted across the Corn Belt now carries the Bt trait to protect against corn rootworm.

Volunteer corn is a weed in soybean fields. In Illinois and the southern Corn Belt, a lot but not all of those kernels will germinate in the fall compared to the North, where none of those downed ears or shelled kernels will germinate. Still, growers have a number of options available to them.

Residual herbicides that control grasses can take out some of the corn volunteers but the residual won't last long enough to take out the majority of volunteers that continue to germinate through the summer. Residual soil herbicides like Du Pont™ Canopy^® and Du Pont™ Classic^®, Pursuit^® Plus or Scepter^® provide some control.

However, post application is the best decision, since you can terminate all the volunteers with a grass herbicide. Post emergence grass herbicides are effective in controlling volunteer corn and include Arrow^®, Assure^® II, Fusilade^® DX, Fusion^®, Poast^®, Poast Plus^®, Select Max^® and Targa^®. These can be tank mixed with glyphosate and other herbicides to knock out tough broadleaves.

Controlling volunteer corn is not a real challenge, but with the adoption of a continuous Roundup Ready rotation, corn volunteers can survive in great numbers. Some growers may choose to leave the volunteer corn to save money if the outbreak isn’t too bad. The downside of that choice is a field that remains unsightly, an increase in rootworm population and a risk to your yield.

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.