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Corn planting may be delayed due to a number of factors, but it is often a result of unfavorable weather conditions. Heavy precipitation may lead to planting into wet soils (Figure 1), 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.
Corn growth and development can be measured by calculating the number of growing degree units (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:
The approximate number of GDUs accumulated by the crop can be estimated to help determine crop growth stage (Table 1).
Figure 1. A flooded field delaying corn planting.
GDU accumulation required for corn development varies with corn product maturity (Table 2). In general, products that require most of the growing season to mature have higher 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.
Careful consideration of several factors should be given prior to switching to an earlier product, including:
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. The intended use for the corn crop can also impact maturity selection. 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 potential GDUs remain in the growing season. This information can help with deciding what maturity to plant and whether or not the corn product should mature before a killing frost (Figure 2). Switching to an earlier-maturing product should only be considered when there is concern with not having enough GDUs left in the growing season.
Once corn planting is delayed, the yield potential of the crop varies with the rest of the growing season. Insect pressure, especially from late generations of European corn borer, corn ear worm, and fall armyworm, can significantly damage a late-planted corn crop. Planting a B.t. corn product can greatly reduce this risk.3 Plant population should reflect the yield expectation and it is important to be very timely with fertilizer applications and weed control as a late-planted corn crop will accumulate heat units faster than an earlier-planted corn crop.
Delayed corn planting may also increase the chance of heat and drought stress during the critical water-use periods (two weeks prior to silking and during pollination). Planting corn products that range in GDU requirements for flowering and physiological maturity can help reduce the chance that the whole corn crop flowers during a period of high heat or is damaged by frost later in the season (Figure 3). Earlier flowering products within the same maturity may be available to help reduce damage from an early frost.
For more information about historical GDU data and planting recommendations, contact your local agronomist or county Extension office.
Figure 2. Estimated normal growing degree days.
Figure 3. Median first frost (32 °F) dates for the continental United States.Source: National Oceanic and Atmospheric Administration. Median first 32 deg F temperature in autumn. http://www.ncdc.noaa.gov/.
Sources: 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