Throughout much of the Midwest, most of the corn is planted, even in Illinois where nearly a week of good weather allowed many farmers to advance well beyond the state’s 10% planted mark confirmed last week. However, continued wet weather has saturated soils and allowed ponds to drown many corn seedlings. In a year when input costs may outstrip commodity sales, most farmers cannot be satisfied with a mediocre stand in the corn field. How do you rationally decide whether to replant, and not waste scarce resources?

Replant decisions are not easy. Are you tearing up field that might have a decent yield just to take a chance that a replanted crop might yield a few more bushels? IL Extension crop specialist Doug Gucker used his newsletter to point out how minimal the population had to be to justify replanting. He says, “If the corn was planted in late April to early May, then the corn stand would need to be less than 13,000 plants per acre to justify replanting.” While his seed and machinery expense are unknown, it is obvious that it would take a very poor stand to warrant the planting expense, plus the yield decline expected from corn that had a month less to grow and mature.

Gucker points to the Illinois Agronomy Handbook for a decision aid that requires you to know the current population, the potential yield for the field, input costs and market value. Such web-based decision aids can make your choice much easier, if they agree with your gut feelings. However, if your gut feeling disagrees with the calculation, then an uneasy choice has to be made.

The University of Nebraska Weekly Cropwatch features a replant guide in its May 22 edition. Crop Specialist Bob Klein and Extension Engineer Paul Jasa give credit to Iowa State University for a couple tables they provide that can assist in the decision. But the NE specialists make the point that “Getting a uniform stand at the right population is an important part of getting a good yield.” The telling part of the Iowa State table is that a planting date between May 26 and June 1 will only provide a 90% yield potential based on a final population of 28-32,000.

Seedling uniformity is a key assessment that you have to make before making any replant decision. Klein and Jasa at Nebraska say, “Research has shown that if one out of six plants is delayed by two leaf stages, yields can be reduced by 4%. If one out of six plants is delayed by four leaf stages, yields can be reduced by more than 8%.” And they remind you to contact your crop insurer, Farm Service Agency, or any others with an interest in your crop before replanting.

Agronomist Roger Elmore at Iowa State University says there are two instances when there is a need to replant. The first is non-uniform emergence, as noted by Klein, and Elmore’s worksheet for lack of uniformity helps you estimate your yield loss, but you have to determine an average for the late plants and an average for the earlier corn plants.
The second situation for replanting needs to be made when populations are significantly less than desired. Elmore’s checklist helps you determine the best course of action. But he warns that replanting may only yield marginal results in a number of situations, such as when one row has not emerged when others have, or when there is a less than two week difference in emergence. In that case he says replanting might only increase the yield by 5% and that would not pay the cost.

At Purdue, corn specialist Bob Nielsen provides much of the same information, but does quite a bit more “virtual hand-holding” to walk you through the steps in making a decision. His methods are quite helpful, and he also raises other issues, such as “patching in” versus complete replanting. He says resist that temptation if your surviving plants are at the two leaf stage or more because they will out-compete the later planted corn. He also suggests that if you replant with an earlier maturing hybrid, it may not meet all of the quality requirements for full season corn if you have contracted for a premium price. And Nielsen says there will be stresses on your late planted corn due to its effort to pollinate in the heat of the summer, and it will be perfectly timed for corn rootworm beetles to feast on its silks and tassels.

Summary:
The decision to replant corn is difficult, given the cost. However, the major issue is whether you are taking a chance to plant a lesser yielding crop than what you may have destroyed. The decision has to be made on the basis of either lack of uniformity of emergence or fewer plants per acre that are viable. Several decision aids are available, however, they are required accurate information on costs and good information on the potential yield of both the old crop and the replanted crop.