Author: Tom Barber, Extension Weed Scientist
Judging by the number of calls I have received this morning, it looks like we will be re-planting some of the March and early April planted corn. The best plan may be to wait for 7 days and take another assessment of the corn stand. This will also allow the existing corn stand to grow to a size easier to kill with herbicide. Corn plants in the spike stage are not that easy to control chemically for several reasons but the number one being coverage. Additionally many seedlings may still be trying to emerge, these can cause issues later in the season if decisions and herbicide applications are made too quickly.
If the decision is made to eliminate the existing corn stand, there are several options that are listed on page 72 of the MP 44. Removing the existing corn stand mechanically with a do-all or similar type of equipment might be possible if enough bed is present for re-plants. Paraquat (Gramoxone 40oz/A, generic 26oz/A ) tank-mixed with atrazine (AAtrex 1pt/A)is a good option when planting back to corn. Similar rates of paraquat can also be tank-mixed with 3 oz/A Sencor or 1pt/A Diuron for equivalent control. Mixtures with paraquat will be more effective with at least 15 GPA and once existing corn reaches the V1 growth stage. With all of these options corn can be re-planted immediately.
Several have asked about Select Max and it will also provide good control of emerged corn at 6 oz/A, keep in mind that there is a minimum 7 day replant behind 6 oz of Select Max. Relative ratings are in the table below, Liberty was evaluated, but with current temperatures in mind Liberty will not be as effective. If you choose to use Liberty, make sure the corn hybrid planted is not Liberty Link. Considering these options I would give these fields a little more time to let remaining corn emerge and re-evaluate the stand. Many times in the past, the best method was using both herbicide and then knocking the rows down to eliminate any seedlings that could still emerge. Keep in mind though if you choose to knock the beds down, you lose any current residual herbicides that have been previously applied. This requires another application following planting of a residual (Dual II Magnum + Atrazine etc.) to prevent early season weed pressure.