University of Nebraska-Lincoln Extension, Institute of Agriculture and Natural Resources

May 19, 2006

Controling volunteer corn in soybean

It is not surprising to see volunteer corn in soybean since the two crops are used in rotation. However, volunteer corn is a weed and should be treated accordingly. It reduces light interception to soybean, interferes with harvesting procedure and makes the field look “messy”. Growth of corn is generally faster than soybean, therefore if it is left uncontrolled, it will overtop the soybean canopy. Control can be achieved by mechanical means (eg. inter-row cultivation) and herbicides.

Timing of inter-row cultivation should depend on the weed pressure. If volunteer corn is a predominant “weed,” cultivation should occur at about the 5-6 leaf stage of corn. Growing point of corn remains in the ground until the 6th leaf stage. Any cultivation prior to that leaf stage may result in regrowth of the plants and will require a second cultivation. It is especially true with shallow cultivation.

If you have Roundup Ready Soybean®, Roundup will control volunteer corn, unless you had Roundup Ready corn the previous year. Roundup will not control volunteer RR corn in RR soybeans.

Herbicides also can be used to effectively control volunteer corn. Several grass type herbicides (graminicides) that can be used at lower rates postemergence in both conventional- and RR-soybean: Assure (4 oz), Fusilade ( 4 oz), Fusion (2 oz), Poast-Plus (10-16 oz), and Select (4 oz). The best control is achieved when herbicides are applied by the third to fourth leaf stage of corn. These herbicides used at full label rates also will control many grassy species, including barnyardgrass, green and yellow foxtail, fall panicum and sandbur.

Stevan Knezevic
Integrated Weed Management Specialist
Haskell Ag Lab, Northeast REC

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Copyright 2006 by the University of Nebraska Board of Regents. All rights reserved.
Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.
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