The 2017 season will be remembered as the “year of replant” by many farmers and seed companies. Replant acres hit record levels in the eastern Corn Belt.

Heading into 2018, Mark Jeschke, agronomy information manager for DuPont Pioneer, looked at corn stand evaluations and replant considerations. His thoughts were published in DuPont Pioneer’s Agronomy Sciences Research Summary.

When the stand isn’t as good as you’d like it to be, take stand counts randomly across the entire area of a field where you’re considering replanting, Jeschke advises. Ask yourself several questions:

• Is the stand consistent across the area?

• Are large gaps present between plants?

• Will the stand have adequate crop canopy to assist with weed control and irrigation efficiencies?

• If you don’t irrigate, will there be sufficient canopy to conserve moisture?

• Will replanting provide an economic gain?

• Are remaining plants healthy and relatively equal in maturity?

Next, compare expected yield from the current stand, based on thousands of plants per acre, to potential yield after replanting and obtaining a higher population. Tables for predicting yield are available in the Purdue University Corn & Soybean Field Guide.

Recognize that an uneven stand will yield less than a relatively even stand with the same number of plants, Jeschke says. Variation in plant size within the row can have a negative effect on yield.

Plants that are severely injured or defoliated will have reduced photosynthetic capability and lower yield potential. Plants with delayed emergence or development are also at a comparative disadvantage. They will have reduced leaf area, less biomass and, therefore, lower yield, Jeschke explains.

Growing degree units
The decision may come down to deciding if there’s enough growing season left to expect the replanted crop to mature. Agronomists often get a handle on this component by looking at growing degree days. The GDD system measures heat units.

If you’ve decided to replant, the next decision may be moving to an earlier hybrid. Jeschke recommends comparing expected growing degree day unit accumulation between planting date and first-frost date to the growing degree unit requirements that the hybrid needs to reach physiological maturity.

Where you live influences the number of GDDs that accumulate after a certain date. See the table below, based on long-term averages, for different parts of Indiana. Numbers may be different in any one season.

One thing working in your favor is that late-planted corn speeds up its maturing process. Bob Nielsen at Purdue University and Peter Thomison at Ohio State University have shown that the total GDD requirement to reach maturity may be up to 200 days less for the same hybrid planted late versus planted early.

Jeschke explains it this way: Late-planted corn shows a reduction in GDD requirements of about six GDD units per day of planting delay.