Prepare for Volunteer Glyphosate-Resistant Corn

Chris Boerboom, Ext. Weed Scientist

Friday, May 26, 2006

We noticed many ears of corn in one of the fields that we were planting this week.  Obviously, this almost guarantees a volunteer corn problem in this particular field.  It may also serve as a reminder for others to do some advance planning for volunteer corn.  Here are a few items that might be worth considering.

There are few options to control volunteer corn in this year’s corn field.  Other than with cultivation, the only way to allow chemical control is to plant a herbicide-resistant hybrid planted that is different from the previous year.  For example, volunteer glyphosate-resistant corn can be controlled in Liberty Link corn or volunteer Liberty-resistant corn can be controlled in glyphosate-resistant corn.  Of course, volunteer conventional corn can be controlled in any herbicide-resistant corn hybrid. 

In soybeans, control options are much better, but it’s best to be prepared and check for volunteer corn before spraying.  For example, if glyphosate was sprayed and glyphosate-resistant volunteer corn was growing in the field, the volunteer corn would not be controlled.  A second herbicide application would be needed just to control the corn.  This would be much more expensive than adding an ACCase herbicide as a tank mix to the glyphosate on the first trip. 

Whether in conventional soybeans or glyphosate-resistant soybeans, the ACCase herbicides that are most effective in controlling corn are Assure II, Select Max (or Select), and Fusion.  Poast Plus is not as active on volunteer corn as the other herbicides.  Glyphosate or any products premixed with glyphosate (Extreme, Sequence) will be very effective on any corn that is not glyphosate resistant.  Raptor is also good at controlling volunteer corn, except for volunteers from Clearfield hybrids.  Pursuit is not as active as Raptor and is generally not satisfactory.

So, while planting, especially soybean fields, did you notice corn ears from last year?  If so, check last year’s planting records to determine if the hybrid was glyphosate-resistant (Roundup Ready) or not.   While scouting soybean fields for weeds, remember to check for volunteer corn. (If people don’t scout for soybeans for weeds anymore because of glyphosate “kills all”, perhaps we should be scouting for volunteer corn).  If volunteer corn exists, check last year’s planting records to determine if the hybrid was glyphosate-resistant (Roundup Ready) or not.  If it was glyphosate-resistant, make plans to tank mix in the appropriate grass herbicide