A lot of farmers have called to ask how to remove unwanted volunteer corn prior to planting wheat this fall. Since about 90 percent of our corn in Arkansas is Roundup Ready, using a burndown treatment of glyphosate is usually not going to work.
This leaves us with tillage as probably the best option. However, most growers are looking for faster, less expensive options. I am not sure we have a real good one.
This situation is similar to the one we faced after the freeze last spring when we needed to remove corn for replanting. I have not done a lot of this work, but we are looking at a few treatments that should work.
The problem is not controlling the corn, although the later into the fall it gets the larger and more difficult to control the corn will be — as long as the growing point is below ground. The problem is following the crop rotational guidelines for wheat.
Most of these labels were not written with immediate plant-back intervals in mind. The two exceptions are Ignite and Gramoxone. Both are fair on removal of volunteer Roundup Ready corn, if the corn has much size to it, both likely will only partially kill the corn. In fact, Ignite may outright fail if the temperatures are too low.
One solution may be to tank-mix Sencor with the Gramoxone. This will basically antagonize the Gramoxone and slow it down, resulting in a more complete kill. You have to worry about whether or not your wheat is sensitive to Sencor, We do not have a real good list. Also, the Sencor label currently has a four-month rotational interval to wheat, even though it is labeled on wheat. Confused?
We are also evaluating some of the graminicides, such as Select, in this situation. If I understand the Select and Select Max labels correctly, technically there is a 30-day rotational interval to wheat. However, I think this treatment would work well.
The other graminicides vary in their labeling. Most do not have soil residual and should not carry over to wheat. I have not done an exhaustive search of these labels for loopholes that might allow for a preplant burndown to wheat. Most were not written this way.
In addition to burndown herbicides, we are also evaluating in-season wheat herbicides for volunteer corn removal. I suspect that some of them may do a fair job on it. Larry Steckle in Tennessee has reported up to 80 percent control of volunteer corn with Finesse, for example. Finesse should be applied at 0.5 ounce per acre, pre to wheat, and you must add a surfactant if you are not tank-mixing it with glyphosate or if the glyphosate does not have a surfactant.
Also, you must plant STS soybeans the year following a Finesse application.
Some fields that I have seen are too grown up to wait to put out a pre or post grass herbicide (such as, Hoelon, Osprey or Axial) after planting the wheat. I am not sure what these will do to volunteer corn.
We have identified a couple of fields with volunteer Roundup Ready corn that we will be placing in studies this fall. I did not have the foresight to see this problem coming. There is a lot more volunteer corn in these fields than I would have thought.
Eventually a freeze will take care of volunteer corn. Some of the fields I have seen, however, will require some action taken just to plant wheat.
Also, there will likely be severe early-season competition between the corn and young wheat. Corn will win until a freeze. But this early-season competition will hurt wheat yields.
Just a final comment on planting wheat following corn: in general it is not a good idea.
First of all, there are fertility and soil compaction issues with following a grass crop with a grass crop. Just ask the guys who planted corn behind rice this year. Granted, I do not expect that wheat following corn will be as bad as corn following rice, but the principal is the same. Be prepared to provide the wheat with a little extra fertilizer.
Also, most of our wheat in Arkansas is treated with atrazine. Planting wheat in the fall after an atrazine application in the previous season is off label and, depending on how much rainfall or irrigation you have had, may injure the wheat.
A few years ago my father had some drift from a sorghum field onto some fallow wheat ground out in Oklahoma. We had pretty much forgotten about it until late in the fall after the wheat came up and you could see a nice drift pattern out in the crop, which never fully recovered.
Atrazine dissipation and carryover to wheat is mainly going to depend on rainfall. It also depends on several other factors, just like planting soybeans after a corn failure in the spring. If I tell you it will be OK, it will be hurt every time. So I am not going to tell you it will be OK.