May 18, 2007

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 for soybean, interferes with harvest and makes the field look "messy." Corn usually gets an early start compared to soybean and if left uncontrolled will overtop the soybean canopy.

Control

Volunteer corn can be controlled mechanically (eg. inter-row cultivation) or with herbicides.

Timing of inter-row cultivation should depend on weed pressure. If volunteer corn is a predominant weed, the timing of cultivation should be at the 5- to 6-leaf stage of corn. Growing point of corn remains in the ground until the 6-leaf stage so any cultivation prior to that stage may result in regrowth and require a second cultivation. It is especially true with shallow cultivation.

If you have Roundup-Ready soybean, Roundup will control volunteer corn, unless you planted Roundup Ready corn the previous year. Roundup will not control volunteer Roundup Ready corn in Roundup Ready soybeans.

Herbicides also can be used to effectively control volunteer corn. Several grass type herbicides (graminicides) can be used at their lower rates postemergence in both conventional and Roundup Ready soybean. Available herbicides and their lower rates includes: Assure (4 oz/ac), Fusilade (4 oz/ac), Fusion (2 oz/ac), Poast-Plus (10-16 oz/ac) and Select (4 oz/ac). Best control is achieved when herbicides are applied by the 3- to 4-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
Extension Weeds Specialist