May 29, 2009

It's 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 harvest and makes the field look "messy." Corn grows faster than soybean so if left controlled, the corn will soon overtop the soybean canopy. Control can be achieved by mechanical means (eg. inter-row cultivation) and herbicides. 

Mechanical Control

Timing of inter-row cultivation should depend on the weed pressure. If volunteer corn is a predominant weed, cultivate at the 5-6 leaf stage of corn. The growing point of corn remains in the ground until the 6th leaf stage. Any cultivation prior to the 6th leaf stage may result in regrowth that will require a second cultivation. This is especially true with shallow cultivation. 

Chemical Control

If you have Roundup Ready® soybean, Roundup® will control the volunteer corn unless you planted Roundup Ready corn the previous year.

Several grass herbicides (graminicides) that can be used at their lower rates postemergence in conventional and Roundup Ready soybean are: Assure (4 oz), Fusilade (4 oz), Fusion (2 oz), Poast-Plus (10-16 oz), and Select (4 oz). Best control is achieved when herbicides are applied by the 3-4th leaf stage of corn.

When used at full label rates, these herbicides also will control many grassy species, including barnyardgrass, green and yellow foxtail, fall Panicum, and sandbur.

Stevan Knezevic, Extension Integrated Weed Management Specialist
Haskell Agricultural Laboratory, Concord