Planting corn later than planned can lead to a shortened growing season and cause you to consider switching to an earlier-maturing corn product. The decision to switch to an earlier-maturing corn product can be difficult due to variations in growing seasons relative to available growing degree units, first fall frost dates, and fall drying conditions.
What to Watch For
Corn planting can be delayed for a number of reasons, but it is often a result of poor weather conditions. Heavy precipitation may lead to planting into wet soils, which can cause uneven stand establishment, poor root development, and sidewall compaction. Delayed planting can also cause a shift in insect and disease pressure, which may result in earlier pesticide application timing. Yield potential for late-planted corn can vary greatly depending on the growing season that follows.
GDU Accumulation and Maturity
The accumulation of heat a corn plant needs to grow from emergence to maturity is often referred to as growing degree units (GDUs). Corn growth and development can be measured by calculating the number of GDUs the crop has accumulated. GDUs are calculated by averaging the daily high (Tmax) and low (Tmin) temperatures minus the base temperature (Tbase), which is set at 50 °F for corn development. Tmax and Tmin are limited to 86 °F and 50 °F, respectively, as the maximum corn growth rate is reached at 86 °F and minimum, if any, corn growth occurs below 50 °F. Daily GDU accumulation can be calculated with the following formula: GDU = ((Tmax + Tmin)/2) - Tbase.1 For example:
- Tmax = 84 ˚F and Tmin = 53 ˚F ((84 + 53)/2) - 50 = 18.5 GDUs
- Tmax = 90 ˚F and Tmin = 65 ˚F ((86 + 65)/2) - 50 = 25.5 GDUs
- Tmax = 83 ˚F and Tmin = 48 ˚F ((83 + 50)/2) - 50 = 16.5 GDUs
By using these values, the approximate number of GDUs accumulated by the crop can be estimated to help determine crop growth stage (Table 1). GDU accumulation required for corn development varies with corn product maturity (Table 2). In general, corn products that require most of the growing season to mature have the highest yield potential. However, if the growing season is shortened due to delayed planting, an earlier maturing product may be needed to avoid having immature grain at the end of the season.
When to Switch Maturities
Carefully consider switching to an earlier maturing product as:
- Full-season corn products for a given area typically have the highest yield potential.
- Daily GDU accumulation is minimal during the planting season when compared to flowering and drydown periods.
- As planting is delayed, corn product maturities move closer together.
- A primary reason for switching to an earlier-maturing corn product is not due to increasing yield potential, but to reduce the risk of immature and wet grain in the fall.
Deciding to plant an earlier-maturing corn product may depend on corn grain prices and grain drying costs.2 With high grain prices and low drying costs, planting an earlier-maturing corn product may not be necessary due to the possible reduction in yield potential. Often the increased yield potential of full-season corn products can outweigh the costs of drying in the fall. If the corn is being planted for silage or high-moisture grain, then the cutoff date to plant an earlier maturing corn product can be later than the cutoff date for corn grain.
Historical GDU accumulation data can help estimate how many GDUs are left in the growing season. Knowing how many potential GDUs are available can help with deciding whether or not the corn product should mature before a killing frost (Figure 1). Switching to an earlier-maturing product should only be considered when there is concern with not having enough GDUs left in the growing season.
Managing Late-Planted Corn
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1 Elmore, R. and Mueller, N. 2015. Growing degree units and corn emergence. University of Nebraska-Lincoln. https://cropwatch.unl.edu/.
2 Corn Agronomy. 2014. Corn late-planting. University of Wisconsin. http://corn.agronomy.wisc.edu/.
3 Heiniger, R. 2004. Management for late planted corn. North Carolina State University. https://www.ces.ncsu.edu/.
Web sources verified 04/12/18. 160502132006