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08
Apr
2013
Killing Existing Corn For Re-Plants
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 a good bit of the March planted corn. I realize that the calendar date has everyone concerned, but there is no need to panic, we haven’t missed a crop yet, and bad decisions now will lead to worse ones later. There has been a lot of work focused on removing corn stands in the past and there are several options to consider. First you need to make sure that most of the corn that has germinated is either up or dead. Judging by calls today, it appears that no one is certain whether an adequate stand will be achieved or not, give it some time. Another reason to hold off on making quick decisions would be the potential 1-2 inches of rain predicted to fall with this storm on Wednesday and the only thing worse than replanting once, is doing it a second time. The best plan is to wait after this rain and take another assessment of the corn stand. This will also allow existing corn 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.

If the decision is made to eliminate the existing corn stand, there are several options that are listed on page 63 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 32oz/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.  Paraquat alone will not effectively kill existing stands.  Mixtures with paraquat will be more effective with at least 15 GPA and once corn reaches the V2 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 corn control ratings are in the table below, Liberty (Ignite) was evaluated and is effective on non-Herculex varieties, but with current temperatures in mind and supply issues I would save Liberty for in-season applications. Considering these options I would give these fields a little more time, at least until after this next big rain and make a decision on Friday.

Other calls regarding weed control in this weak/sick corn crop have been asked and in most cases the answer has been an application of Roundup or glyphosate only to control existing weeds. The large majority of these are annual bluegrass, other grasses and maybe some small henbit. I have not received one call on pigweed yet……Once the corn begins to grow then come back with a second application consisting of glyphosate and residual herbicides including metolachlor and atrazine or pre-mix such as Halex GT with atrazine. Many products and combinations exist for excellent weed control in corn, but with the corn growing off slow, any competition from weeds early will result in lost yield at harvest. If corn health and herbicide injury are a concern, go ahead with glyphosate application now and come back in 7-14 days with the multiple mode of action residual herbicide combination.

corn removal slide 2

 

 

 

 

 

 


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