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Less than ideal weather conditions led to many acres of late planted and even replanted corn across the region. While planting decisions have all been made and corn is now in the ground, there is still a lot of uncertainty and concern about the yield potential for late-planted corn.
The yield potential of corn is a moving target. Even corn planted under ideal soil conditions and planting date is not assured of reaching top-end yield potential. There are many yield-influencing factors that occur throughout the growing season that have the potential to affect the ultimate outcome.
Delayed planting can put a corn crop at greater risk from certain factors. Later planted corn can be more susceptible to late July and early August heat because it is more likely to be flowering during that time period due to the delay.1 Weather conditions during pollination are one of the most influential factors in determining yield potential.
Corn rootworm beetles may be drawn to later planted corn during pollination, especially if nearby corn that was planted on time has already flowered. It may also attract second-generation ECB moths resulting in the subsequent ECB larval damage.1 A couple weeks difference in planting can also cause diseases to take hold earlier in the growing season causing infection at earlier, more vulnerable stages.2 For instance, late-planted corn can be more susceptible to yield loss from gray leaf spot (GLS) because it would be infested at an younger growth stage than earlier-planted corn.1
Scouting later planted corn is a necessity. Be sure to monitor potential disease outbreaks and take action early to help maintain yield potential. For example, GLS and Northern corn leaf blight (NCLB) are common diseases that may be treated with a timely fungicide application when caught early.2 Consider all crop inputs and do the best to capture the crop’s remaining yield potential by monitoring soil conditions, fertility, and insect and disease pressure.
As planting is delayed, corn product maturities will come closer together. Growing degree unit (GDU) accumulation increases as the growing season progresses. As a result, corn generally requires around 6.8 GDUs less each day to reach physiological maturity (black layer) as planting is delayed beyond about May 1.4 This means that late-planted products mature in fewer than expected GDUs. Therefore, corn planted in late May compared to an optimum date may actually take 125 to 200 GDUs less to reach black layer.
A study conducted by Cornell University compared corn product response to mid-May versus late-April planting dates. The results indicated that there was very limited, if any, yield loss with corn planted mid-May compared to that planted the last week of April. However, grain moisture may be around 2 percentage points higher at harvest.5
Table 1 (page 3) shows information from Penn State regarding the percentage of maximum yield potential expected based on plant stand, planting date, and yield environment.
Table 1. Penn State Percent of Maximum Yield Expected Based on Final Plant Stands and Planting Dates in Various Yield Environments.
Sources: 1Nielsen, R.L. 2003. Estimating yield and dollar returns from corn replanting. AY-264-W. Purdue Extension. www.agry.purdue.edu. 2Nielsen, R.L. 2018. The Planting Date Conundrum for Corn. Corny News Network. Purdue University. www.agry.purdue.edu. 3Begemann, S. 2018. Yield Threats for Later Planted Corn. Ag Web. www.agweb.com. 4Nielsen, R.L. 2017. Hybrid Maturities for Delayed Planting. Purdue University. www.agry.purdue.edu. 5Cox, W. and P. Atkins. 2011. A broad optimum planting date for corn? What’s Cropping Up? Vol. 21 No. 1. Cornell University. http://css.cals.cornell.edu. Web sources verified 6/6/18. 180605160236