Late fall planting, harsh winter conditions and/or excessive rainfall can all lead to an undesirable wheat stand in the spring. Often growers would like to turn those failed wheat acres into a corn field and questions arise as to how to best ensure a successful transition.
The transition starts with killing the existing wheat stand to avoid the competition of early season weeds. Then nutrient management and the intricacies associated with the existing nutrients and future nutrient recommendations need to be addressed. Growers then need to identify tools and keys to ensure a successful stand establishment is obtained. In addition, insect pressure is greater in volunteer wheat stands and need to be controlled to ensure a prosperous corn crop.
The first step is to kill the remaining wheat crop prior to planting the corn. Corn is very sensitive to early season competition and killing the growing wheat will eliminate that competition. The most effective method to kill the wheat crop is through the use of herbicides. The two best options include a glyphosate (1.5 pounds active ingredient per acre) + 2,4-D (1-2 pints per) program and a Gramaxone (3-4 pints per) + atrazine (1.5 pound active ingredient per acre) + 2,4-D (1-2 pints per acre) program. The Gramaxone based option is more expensive but does provide a faster burndown for immediate planting. Also when growers will be trying to kill a wheat stand the temperatures could be colder and the Gramaxone based system is less sensitive to cooler temperatures than the glyphosate program.
When using an herbicide program to kill the wheat stand, the best timing simply is the earlier the better. By killing the stand earlier less moisture is lost from the seedbed; the decomposition process is sped up and will reduce the negative effects of allelopathic (Allelopathy is the biological process where plants produce chemicals that influence growth, survival and reproduction of other plants) substances found in the decaying wheat. The second option to kill a stand of wheat is by tillage. With tillage come several obstacles, moist soil conditions and the “chemical” effect on the young corn plant. When most wheat fields need tilled the soil conditions are often wet and will be difficult to work and create an ideal seed bed. The second obstacle begins when the residue is worked into the soil. The decaying residue begins to tie up all available nitrogen as microbes do their job. Also as the residue decomposes it releases allelopathic substances that can slow the growth of young corn plants. To best maximize the tillage pass, set tillage tool as shallow as possible and keep the soil profile firm to reduce moisture evaporation.
A portion of the nitrogen that was applied to the wheat crop will be available to the new corn crop. The challenge is determining how much nitrogen actually remaining. The amount that is remaining can vary depending on the source of nitrogen, the amount of rainfall the field has received and the recent temperatures. Warm, wet weather with ponding occurring is a recipe for high nitrogen loss. If the wheat crop is frost killed, a majority of the nitrogen will be available throughout season.
To determine the amount of nitrate nitrogen available to the growing corn crop, consider taking a Presidedress Soil Nitrate Test (PSNT). A PSNT should be taken when corn is at the four to six leaf stage, just ahead of the sidedress application of nitrogen. The PSNT is designed to estimate the amount of nitrate nitrogen that is available in the soil. If the PSNT reports more than 25 parts per million nitrate nitrogen, no additional nitrogen is recommended.
When planting into a failed wheat crop, a majority of the soil nitrogen will initially be tied up by microorganisms that are breaking down the wheat residue. To successfully balance the tie up of soil nitrogen and the young corn plants need for nitrogen, a starter with nitrogen is recommended or applying additional pre plant nitrogen via UAN solution will meet the early season corn crops nitrogen needs.
Wheat is a grass crop just like corn and there is a potential for grass loving insects such as black cutworm, wireworm and armyworms to have a huge impact on the young corn crop. As the wheat crop begins to die and decay the insects will move from the wheat to the corn and begin feeding on it. The “greener” the wheat crop is at planting the more potential for insect damage in the corn. The best options for insect control is one, wait until the wheat crop is brown before planting, which would be approximately two weeks after the herbicide application, or two, use an insecticide with the herbicide to stop or slow whatever insects are present. Also consider using a seed treatment package that will provide protection for any wireworm infestations.
Any herbicide applied to the wheat crop could pose a concern for carryover. Some herbicides will not allow another crop to be planted that season, while others have a set interval of days between application and planting the next crop. Refer to the label of any herbicides that were applied to the wheat crop to ensure there will be no herbicide concerns. Always read and follow label directions.