Replant Intervals for Common Corn Pre- and Post-Emergence Herbicides
Determining how to control the existing stand and deciding whether to replant to corn or switch to another crop will likely be affected by previous decisions you've made. For example, if a corn specific herbicide with residual activity was applied this spring, planting soybeans may no longer be an option.
At this point in the season, replanting corn is still the most desirable option in most cases. If a corn preemergence herbicide already was applied, options for planting a crop other than corn may be limited.
Consider the planting date and choose an appropriate corn hybrid. You’ll likely need to plant a shorter season hybrid than you originally planted. In some situations, soybeans or grain sorghum may be an option. See the Replant Intervals Table for common corn pre- and post-emergence herbicides for replanting to corn, soybeans, or grain sorghum.
Killing a Poor Corn Stand for Replant Purposes
Mechanical Control
Cultivation can be effective, but it has to be done when soil and weather conditions are right. Also, depending on the cultivation method, complete control of the existing stand may not happen. Until about the V5 growth stage, the growing point of the corn plant is still below ground, making it more difficult to control the plant with some types of cultivation.
Chemical Control
This method, while effective in many cases, is not bullet proof. Once you decide to destroy a poor corn stand, the existing crop becomes a volunteer corn problem.
Glyphosate will provide excellent control of poor conventional or Liberty Link corn stands. If the corn stand has only the Roundup Ready trait and you plan to replant to corn, there are three options for controlling the stand: Ignite (glufosinate), Gramoxone (paraquat), or Select Max (clethodim). Select Max has a supplemental label allowing the replanting of corn six days after application.
Other ACCase herbicides, such as Assure II, Fusilade DX, or Fusion, will control an existing corn stand, however the labeled replant interval is too long for these to be considered viable options at this point. If the corn is stacked with Roundup Ready and Liberty Link traits, consider Gramoxone or Select Max.
Ignite has no residual activity and will not be an effective option if the seed corn has the Liberty Link trait. UNL research indicates that under cool, dry conditions this option may provide inconsistent control. To maximize effectiveness add AMS and use the appropriate spray volume (15 to 20 GPA).
Gramoxone is similar to Ignite and has no residual activity. This herbicide is a contact herbicide and will show very little translocation, especially if applied on a sunny day. Gramoxone is a fast-acting herbicide. Depending on weather, herbicide activity may be evident in the first area of application in the field before the last area is finished. Gramoxone activity may be enhanced by tank-mixing it with atrazine or metribuzin.
ACCase inhibitors are often slow acting, but generally provide good, consistent control of the corn stand. If replanting corn in the field, these herbicides have plant-back restrictions so consult the label before applying these herbicides.
Greg Kruger, Extension Croping Systems Specialist
West Central REC, North Platte
Lowell Sandell
Extenstion Educator – Weeds, Lincoln
