As the rains continue to delay corn planting progress, more concerns are rising regarding the appropriate “cut-off” date for planting corn. Fortunately, we have recently completely a research initiative at Mississippi State University on this very subject. The primary objective of this research was to evaluate the yield response of modern corn hybrids, possessing Bt technology for corn borer protection, to well later than normal planting dates. Thus, we can utilize this information to make better cropping decisions, particularly when rainfall delays planting, or we are faced with replanting decisions.
Irrigated field studies were conducted in 2009, 2010 and 2011 at the MSU Delta Research and Extension Center at Stoneville and the RR Foil Research Center at Mississippi State University using the furrow irrigation method. Corn produced optimal grain yields until about May 1, when productivity began to decline. Corn yield loss was quite moderate through May, until declining quickly in June. The magnitude of irrigated corn yield reduction associated with planting beyond the optimum time frame was 1.3 bu. per day or 0.76% per day for plantings during May and increased to 2.1 bu. per day or 1.59% per day for June plantings.
The numbers on the X-axis in the figures below represent the Julian date of the year (75=March 15, 165=June 13). The trendline shows the response of five hybrids (each represented by a different color) planted at 2 – 2 ½ week intervals over the duration of the study.
These results indicate a couple substantial findings.
- Foremost, yield reduction associated with late-planted irrigated corn initially gradually declines and escalates with time. However, irrigated corn productivity does not abruptly nose-dive during May. Thus, there is little justification to “cut-off” or completely abandon corn planting intentions, if planting is slightly delayed past optimum dates.
- Also, these results show irrigated corn may produce optimum yields about 10 days later than our established MSU Extension Service guidelines, which differ depending upon latitude regions of our state.
Dryland studies were conducted at the RR Foil Research Center at Mississippi State University in 2010, 2011 and 2012. Corn planted at later dates in dryland culture suffered more consistent yield loss than irrigated corn. However, pollination failure or catastrophic yield loss never occurred, despite corn being exposed to two of the most severe drought seasons in Mississippi history during 2010 and 2011. The magnitude of dryland corn yield reduction was 1.3 bu. per day or 0.83% per day for plantings after Mid-April. Although substantial, this productivity loss was relatively moderate and not substantially different from Corn Belt studies.
The numbers on the X-axis in the figure below represent the Julian date of the year (95=April 4, 155=June 3). The trendline shows the response of five hybrids (each represented by a different color) planted at 2 – 2 ½ week intervals over the duration of the study.
Therefore, I believe there is little reason for alarm, as we still have considerable time to plant corn, particularly if you have irrigation capability. Optimum corn planting dates and response trends associated with late plantings are expected to be likely 7-14 days later in northernmost Mississippi counties, compared to the research conducted near the Highway 82 latitude noted above.
It is much more important to utilize Bt technology for insect protection when planting late, so try to use those traits with lower refuge requirement (20%) when doing so. I also suggest reducing your seeding rate for late plantings, because late corn generally develops more height and leaf area. This will also help alleviate the effect of drought stress, particularly for dryland production.