What are the Yield Expectations of May Planted Corn?

by Jason Kelley, Professor and Extension Agronomist - Wheat and Feed Grain - May 10, 2021

This year’s planting season has been a challenge for some to get corn (and other crops) planted due to persistent untimely rains.  Areas of East-Central and Northeast Arkansas seem to be the areas lagging behind the most on planting.  Statewide we have made good planting progress with an estimated 85% of the anticipated corn acres already planted (NASS report, May 3^rd).  With the huge increases in corn prices over the last few weeks, the push to get corn planted is greater than in most years, even though we are at the end of the typical planting window.  Some producers still anticipate planting the rest of their intended corn acres and are wondering about yield potential and production issues. 

So, what is the yield potential of corn planted in Mid-May or later?  I think most realize at this point in May that yield potential is dropping every day.  From our planting date studies and other trials that were conducted in past years, yields of irrigated corn start dropping in late April or early May depending on what part of the state you are located in.  At Marianna, Arkansas (East-Central), in an 8-year planting date study (2008-2015) corn planted prior to May 1 on average achieved 100% of maximum yield potential most years.  Corn yields slowly declined each week when planting was delayed after May 1.  Below are average % relative yields for each week in May at Marianna from planting date studies.          

A field with a 200 bu/acre yield history in past years, when planted May 20^th would have an approximate 85% yield potential or roughly an estimated 170 bu/acre potential, provided best management practices are implemented timely and everything is adequate for optimum yields (BEST CASE SCENERIO).

In our corn research verification program, we have a limited number of corn fields that have been planted in May (nine fields) in recent years.  Planting dates and corresponding yields for those fields are shown below.  These yields are from whole field averages and were produced following normal extension recommendations.  

May Planted Corn Research Verification Fields and Yields (2008 - 2020)

This data highlights that good yields can be realized with late planting with proper management, but also highlights that yield variability can be seen.  The importance of timely inputs and proper irrigation with late planted corn is very important to achieve maximum yield potential.  

How Does Late Planting Impact Corn Growth and Development?

In general corn develops at a much faster rate in late plantings than early planting due to rapid accumulation of heat units.  Inputs such as herbicides and sidedress nitrogen will occur much quicker after planting compared to a typical March or April planting.  Below is how late planted corn developed compared to earlier planting dates in a planting date study at Marianna, Arkansas with a wide range of planting dates.  Keep in mind, heat unit accumulation will dictate how rapid corn growth is. 

*Dates of harvest with corn at approximate 18% grain moisture.  Days to harvest can vary greatly depending on drying conditions after maturity.  Hybrid relative maturity will also have an impact on harvest date.   

Management Considerations

Hybrid Maturity and Selection:  In past studies, yields of hybrids with a relative maturity of 114-120 days generally provided greater yields than earlier maturity hybrids of 110 day or less.  However, keep in mind that the drydown period for late planted corn will be in September and field drying may be slow during this time, especially for full season hybrids.  A harvest date for a 114-day maturity hybrid at 18% grain moisture compared to 120-day hybrid would likely be a week or more different if field drying.      

Another consideration is plant height and lodging resistance.  Late planting generally leads to taller plants compared to early plantings and that can increase lodging potential.  Extremely tall hybrids or hybrids that are prone to late-season lodging should be avoided. 

Plant population:  A recommended final plant population of approximately 32,000 plants/acre is still desired with late planting, however with late planting a higher percentage of plants may emerge, so the seeding rate may be able to be reduced slightly and still reach the desired population.  Planting 36-38K seeds/acre may unnecessarily increase late-season lodging potential for some hybrids.    

Irrigation:  Timely and proper irrigation is needed for successful late planted corn most years.  Typically, from past experiences, May planted corn often requires 1 or 2 more furrow irrigations or 2-3 pivot irrigations compared to a normal late March or early April planting date. 

Foliar Fungicide:  Foliar diseases such as southern rust will more likely have a potential to be a yield limiting factor in late planted corn.  Typically, March or April planted corn may “outrun” southern rust, but with corn maturity pushed back, the risk of southern rust being a yield reducer is real.  Budget for a foliar fungicide application for disease control. 

**For additional information, please contact your local county extension agent.