Due to the cold wet weather we experienced in late April and early May, corn planted in April has struggled to emerge in many areas of the state. There are also some fields planted where standing water may result in poor corn stand establishment due to poor water drainage. Therefore, there are a number of fields that may need to be replanted. The purpose of this article is to discuss the options to kill an existing stand of corn in a replant situation.
The first issue to address is what herbicide resistance traits are stacked in the corn you would like to remove from the field. If the corn is non-GMO (no herbicide-resistance traits), your options for control are tillage, glyphosate (e.g. Roundup, others), clethodim (e.g. Select Max, others), paraquat (e.g. Gramoxone) + metribuzin (e.g. Tricor, others), or glufosinate (e.g. Liberty, others). The best solution to control non-GMO corn will be to use tillage or glyphosate. Non-GMO corn is very sensitive to glyphosate and no waiting interval is needed to replant. You can also use glyphosate or tillage to control Liberty Link corn hybrids (as long as the hybrid is not also Roundup Ready).
For Roundup Ready corn that doesn’t carry the Liberty Link trait, tillage, clethodim, or paraquat + metribuzin (Gramoxone + Tricor) would be the logical methods for termination. Another option for corn that is not Liberty Link is to replant a Liberty Link corn hybrid and apply a follow-up treatment of glufosinate (Liberty) postemergence to control plants that survived the first application.
The use of 32 to 34 oz/A of Liberty has been effective for the control of small corn (V1 to V3) in our research. Keep in mind that we are facing a herbicide shortage situation this growing season and certain products have inflated costs or may not be readily available at your ag retailer.
If the corn to be terminated is GMO, then the options are somewhat more complicated. Many popular commercial hybrids are stacked with either Roundup Ready and Liberty Link traits, or both. If you have corn stacked with both traits, our experience has been that tillage will be the most reliable method, and would not have the waiting interval associated with clethodim, but tillage is not desirable for those in a long-term no-till situation or those with cover crops in the field.
Numerous clethodim products, including Select Max, can be used to control the stacked trait corn in a replant situation. The use of Select Max will provide better corn control than Gramoxone + Tricor, but it requires a waiting interval of 6 days after the field is treated with Select Max. The directions on the label indicate that up to 6 fl oz/A can be applied plus 0.25% NIS and 2.5 to 4 lb/A of AMS as the spray additives.
Apply to corn that is 12 inches or less. Avoid overlapping the boom as overlaps may result in excessive crop injury. Growers should also be aware that broadleaf herbicides such as 2,4-D or dicamba (group #4) can antagonize the activity of clethodim and result in reduced control of volunteer corn.
Another option to control “volunteer” corn stacked with both the Liberty Link and Roundup Ready traits is to plant corn containing the Enlist trait. Enlist corn hybrids are resistant to the ACCase-inhibiting herbicides (Group #1) in the aryloxyphenoxypropionate family (FOPs) such as Assure II (quizalofop) herbicide. Assure II is the only FOP herbicide labeled for POST applications to Enlist corn. Spray Assure II (quizalofop) at 5-12 fl oz/A (plus 1% v/v of COC or 0.25% v/v of NIS) when the Enlist corn is between the V2-V6 growth stages.
If you want to avoid the preplant interval for clethodim and will not plant Enlist corn, your only herbicide option for termination of stacked trait corn is paraquat plus metribuzin. In University research trials, 2-3 pt/A of Gramoxone plus 4-6 oz/A of dry metribuzin (e.g. Tricor, others) has been effective for control of small corn (V1 to V3). Application of Gramoxone alone, without the addition of metribuzin, is likely to be less effective. Corn that has advanced past the V3 growth stage will generally be more difficult to control.
The information listed here is based on research and outreach extension programming at Purdue University and elsewhere. The use of trade names is for clarity to readers of this site, it does not imply endorsement of a particular brand nor does exclusion imply non-approval. Always consult the herbicide label for the most current and updated precautions and restrictions.