Due to the recent cold wet weather, corn planted in April has either struggled to emerge or the corn that did emerge may have been injured by frost events or it looks bad because of the cold weather. There are also some fields planted in early May where standing water may result in poor corn stands due to poor water drainage. Therefore, there are a number of fields which 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, others) + 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 intervals are 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, Select Max, or paraquat + metribuzin (Gramoxone + Tricor) would be the logical methods for termination. Another option for corn that is not Liberty Link is to replant Liberty Link corn and apply a follow up treatment of Liberty postemergence to control plants that survived the first application. Use of 32 to 34 oz/A of Liberty has been effective for control of small corn (V1 to V3) in our research.
If your corn is NOT non-GMO, then the options are somewhat more complicated. Many popular commercial hybrids are stacked with either Roundup Ready and Liberty Link traits, or both traits. 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 Select Max, 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 synthetic auxin herbicides such as 2,4-D or dicamba can antagonize the activity of clethodim and other ACCase-inhibiting herbicides and result in reduced control of volunteer corn. Additionally, tank-mixing acetochlor with dicamba applications can accentuate the antagonistic effect of dicamba and reduce clethodim efficacy for “volunteer” corn control even further. Figures 1 and 2 demonstrate the antagonistic effect of dicamba and dicamba + acetochlor on the control of “volunteer” corn with clethodim in an Xtend soybean field. Split applications of auxinic herbicides (2,4-D or dicamba) and clethodim would be the only alternative to prevent herbicide antagonism when using these herbicides, since increasing the rate of clethodim would also extend the preplant interval for corn replant.
Another option to control “volunteer” corn stacked with both the Liberty Link and Roundup Ready traits is to plant Enlist corn and 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. Enlist corn is resistant to ACCase-inhibiting herbicides in the aryloxyphenoxypropionate family (FOPs) such as Assure II, which is the only FOP herbicide labeled for POST applications to Enlist corn.
If you want to avoid the waiting interval to plant for clethodim and will not plant Enlist corn, your only herbicide option for termination of stacked trait corn is paraquat + metribuzin. In University research trials, 2-3 pt/A of Gramoxone + 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.
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 update precautions and restrictions.
Figure 1. Antagonistic effect of dicamba and acetochlor on corn control with Clethodim 2EC. Abbreviations: XM = XtendiMax (22 oz/A); RUP = RoundUp PowerMax II (32 oz/A); WAR = Warrant (48 oz/A).
Figure 2. Antagonistic effect of dicamba and dicamba + acetochlor on corn control with Clethodim 2EC. Abbreviations: XM = XtendiMax (22 oz/A); RUP = RoundUp PowerMax II (32 oz/A); WAR = Warrant (48 oz/A).
